Standards Track Work Product
OData Extension for Data Aggregation Version 4.0 Committee Specification 04 18 November 2025
This stage: https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs04/odata-data-aggregation-ext-v4.0-cs04.md (Authoritative) https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs04/odata-data-aggregation-ext-v4.0-cs04.html https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs04/odata-data-aggregation-ext-v4.0-cs04.pdf Previous stage: https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs03/odata-data-aggregation-ext-v4.0-cs03.md (Authoritative) https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs03/odata-data-aggregation-ext-v4.0-cs03.html https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs03/odata-data-aggregation-ext-v4.0-cs03.pdf Latest stage: https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/odata-data-aggregation-ext-v4.0.md (Authoritative) https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/odata-data-aggregation-ext-v4.0.html https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/odata-data-aggregation-ext-v4.0.pdf Technical Committee: OASIS Open Data Protocol (OData) TC Chairs: Ralf Handl ([email protected]), SAP SE Michael Pizzo ([email protected]), Microsoft Editors: Ralf Handl ([email protected]), SAP SE Hubert Heijkers ([email protected]), IBM Gerald Krause ([email protected]), SAP SE Michael Pizzo ([email protected]), Microsoft Heiko Theißen ([email protected]), SAP SE Martin Zurmuehl ([email protected]), SAP SE Additional artifacts: This document is one component of a Work Product that also includes: ABNF components: OData Aggregation ABNF Construction Rules Version 4.0 and OData Aggregation ABNF Test Cases: https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/cs04/abnf/ OData Aggregation Vocabulary:
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 1 of 69
Standards Track Work Product
https://docs.oasis-open.org/odata/odata-data-aggregationext/v4.0/cs04/vocabularies/Org.OData.Aggregation.V1.json https://docs.oasis-open.org/odata/odata-data-aggregationext/v4.0/cs04/vocabularies/Org.OData.Aggregation.V1.xml Related work: This specification is related to: OData Version 4.01. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. A multi-part Work Product which includes: OData Version 4.01 Part 1: Protocol. Latest stage: https://docs.oasis-open.org/odata/odata/v4.01/odatav4.01-part1-protocol.html OData Version 4.01 Part 2: URL Conventions. Latest stage: https://docs.oasisopen.org/odata/odata/v4.01/odata-v4.01-part2-url-conventions.html ABNF components: OData ABNF Construction Rules Version 4.01 and OData ABNF Test Cases. https://docs.oasis-open.org/odata/odata/v4.01/os/abnf/ OData Vocabularies Version 4.0. Edited by Michael Pizzo, Ralf Handl, and Ram Jeyaraman. Latest stage: https://docs.oasis-open.org/odata/odata-vocabularies/v4.0/odata-vocabularies-v4.0.html OData Common Schema Definition Language (CSDL) JSON Representation Version 4.01. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. Latest stage: https://docs.oasis-open.org/odata/odata-csdljson/v4.01/odata-csdl-json-v4.01.html OData Common Schema Definition Language (CSDL) XML Representation Version 4.01. Edited by Michael Pizzo, Ralf Handl, and Martin Zurmuehl. Latest stage: https://docs.oasis-open.org/odata/odata-csdl-xml/v4.01/odata-csdlxml-v4.01.html OData JSON Format Version 4.01. Edited by Ralf Handl, Mike Pizzo, and Mark Biamonte. Latest stage: https://docs.oasis-open.org/odata/odata-json-format/v4.01/odata-json-format-v4.01.html Abstract: This specification adds basic grouping and aggregation functionality (e.g. sum, min, and max) to the Open Data Protocol (OData) without changing any of the base principles of OData. Status: This document was last revised or approved by the OASIS Open Data Protocol (OData) TC on the above date. The level of approval is also listed above. Check the “Latest stage” location noted above for possible later revisions of this document. Any other numbered Versions and other technical work produced by the Technical Committee (TC) are listed at https://groups.oasis-open.org/communities/tc-community-home2?CommunityKey=e7cac2a9-2d18-4640-b94d018dc7d3f0e2#technical. TC members should send comments on this specification to the TC’s email list. Any individual may submit comments to the TC by sending email to [email protected]. Please use a Subject line like “Comment on OData Data Aggregation”. This specification is provided under the RF on RAND Terms Mode of the OASIS IPR Policy, the mode chosen when the Technical Committee was established. For information on whether any patents have been disclosed that may be essential to implementing this specification, and any offers of patent licensing terms, please refer to the Intellectual Property Rights section of the TC’s web page (https://www.oasis-open.org/committees/odata/ipr.php). Note that any machine-readable content (Computer Language Definitions) declared Normative for this Work Product is provided in separate plain text files. In the event of a discrepancy between any such plain text file and display content in the Work Product’s prose narrative document(s), the content in the separate plain text file prevails. Key words: The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”, “MAY”, and “OPTIONAL” in this document are to be interpreted as odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 2 of 69
Standards Track Work Product
described in BCP 14 [RFC2119] and [RFC8174] when, and only when, they appear in all capitals, as shown here. Citation format: When referencing this specification the following citation format should be used: [OData-Data-Agg-v4.0] OData Extension for Data Aggregation Version 4.0. Edited by Ralf Handl, Hubert Heijkers, Gerald Krause, Michael Pizzo, Heiko Theißen, and Martin Zurmuehl. 18 November 2025. OASIS Committee Specification 04. https://docs.oasisopen.org/odata/odata-data-aggregation-ext/v4.0/cs04/odata-data-aggregation-ext-v4.0-cs04.html. Latest stage: https://docs.oasis-open.org/odata/odata-data-aggregation-ext/v4.0/odata-data-aggregation-ext-v4.0.html. Notices Copyright © OASIS Open 2025. All Rights Reserved. Distributed under the terms of the OASIS IPR Policy. The name “OASIS” is a trademark of OASIS, the owner and developer of this specification, and should be used only to refer to the organization and its official outputs. For complete copyright information please see the full Notices section in an Appendix below.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 3 of 69
Standards Track Work Product
Table of Contents 1 Introduction 1.1 Changes from Earlier Versions 1.2 Glossary 1.2.1 Definitions of Terms 1.2.2 Acronyms and Abbreviations 1.2.3 Document Conventions 2 Overview 2.1 Example Data Model 2.2 Example Data 2.3 Example Use Cases 3 System Query Option $apply 3.1 Fundamentals of Input and Output Sets 3.1.1 Type, Structure and Context URL 3.1.2 Sameness and Order 3.1.3 Evaluation of Data Aggregation Paths 3.2 Basic Aggregation 3.2.1 Transformation aggregate 3.2.1.1 Aggregation Algorithm 3.2.1.2 Keyword as 3.2.1.3 Aggregation Methods 3.2.1.3.1 Standard Aggregation Method sum 3.2.1.3.2 Standard Aggregation Method min 3.2.1.3.3 Standard Aggregation Method max 3.2.1.3.4 Standard Aggregation Method average 3.2.1.3.5 Standard Aggregation Method countdistinct 3.2.1.3.6 Custom Aggregation Methods 3.2.1.4 Aggregate Expression $count 3.2.2 Transformation concat 3.2.3 Transformation groupby 3.2.3.1 Simple Grouping 3.3 Transformations Producing a Subset 3.3.1 Top/bottom transformations 3.3.1.1 Transformations bottomcount and topcount 3.3.1.2 Transformations bottompercent and toppercent 3.3.1.3 Transformations bottomsum and topsum 3.3.2 Transformation filter 3.3.3 Transformation orderby 3.3.4 Transformation search 3.3.5 Transformation skip 3.3.6 Transformation top 3.3.7 Stable Total Order Before $skip and $top 3.4 One-to-One Transformations 3.4.1 Transformation identity 3.4.2 Transformation compute 3.5 Transformations Changing the Input Set Structure odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 4 of 69
Standards Track Work Product
3.5.1 Transformations join and outerjoin 3.6 Expressions Evaluable on a Collection 3.6.1 Function aggregate 3.6.2 Expression $count 3.7 Function isdefined 3.8 Evaluating $apply as an Expand and Select Option 3.9 ABNF for Extended URL Conventions 4 Cross-Joins and Aggregation 5 Vocabulary for Data Aggregation 5.1 Aggregation Capabilities 5.2 Custom Aggregates 5.3 Context-Defining Properties 5.4 Annotation Example 5.5 Hierarchies 5.5.1 Recursive Hierarchy 5.5.1.1 Hierarchy Functions 5.5.2 Hierarchy Examples 5.6 Functions on Aggregated Entities 6 Hierarchical Transformations 6.1 Common Parameters for Hierarchical Transformations 6.2 Hierarchical Transformations Producing a Subset 6.2.1 Transformations ancestors and descendants 6.2.2 Transformation traverse 7 Examples 7.1 Requesting Distinct Values 7.2 Standard Aggregation Methods 7.3 Requesting Expanded Results 7.4 Requesting Custom Aggregates 7.5 Aliasing 7.6 Combining Transformations per Group 7.7 Model Functions as Set Transformations 7.8 Controlling Aggregation per Rollup Level 7.9 Aggregation in Recursive Hierarchies 7.10 Maintaining Recursive Hierarchies 7.11 Transformation Sequences 8 Conformance A References A.1 Normative References B Acknowledgments B.1 Special Thanks B.2 Participants C Revision History D Notices
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 5 of 69
Standards Track Work Product
1 Introduction This specification adds aggregation functionality to the Open Data Protocol (OData) without changing any of the base principles of OData. It defines semantics and a representation for aggregation of data, especially: Semantics and operations for querying aggregated data, Results format for queries containing aggregated data, Vocabulary terms to annotate what can be aggregated, and how.
1.1 Changes from Earlier Versions Compared to the previous stage [OData-Data-Agg-v4.0] OASIS Committee Specification 03, this version makes the following restrictions. Section
Restriction
After section 3.2.1.4
Keyword from removed
After section 3.2.3.1
Grouping with rollup removed
After section 3.4.2
Transformation addnested removed
After section 3.5.1
Transformation nest removed
Before section 5.5.1
Leveled Hierarchy removed
Section 6.1
Optional parameter S removed
Section 6.2.2
Restricted to single-valued ParentNavigationProperty
After section 6.2.2
Grouping with rolluprecursive removed
1.2 Glossary 1.2.1 Definitions of Terms This specification defines the following terms: Aggregatable Expression – an expression not involving term casts and resulting in a value of a complex or entity or an aggregatable primitive type Aggregate Expression – argument of the aggregate transformation or function defined in section 3.2.1.1 Aggregatable Primitive Type – a primitive type other than Edm.Stream or subtypes of Edm.Geography or Edm.Geometry Data Aggregation Path – a path that consists of one or more segments joined together by forward slashes (/). Segments are names of declared or dynamic structural or navigation properties, or type-cast segments consisting of the (optionally qualified) name of a structured type that is derived from the type identified by the preceding path segment to reach properties declared by the derived type. Expression – derived from the commonExpr rule (see [OData-ABNF]) Single-Valued Property Path – property path ending in a single-valued primitive, complex, or navigation property
1.2.2 Acronyms and Abbreviations The following non-exhaustive list contains variable names that are used throughout this document: A, B, C – collections of instances
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 6 of 69
Standards Track Work Product
H – hierarchical collection H ′ – subset of nodes from a hierarchical collection u, v, w – instances in a collection x – an instance in a hierarchical collection, called a node p, q, r – paths T – transformation sequence α – aggregate expression, defined in section 3.2.1.1 Γ(A, p) – the collection that results from evaluating a data aggregation path p relative to a collection A, defined in section 3.1.3 γ(u, p) – the collection that results from evaluating a data aggregation path p relative to an instance u, defined in section 3.1.3 ΠG(s) – a transformation of a collection that injects grouping properties into every instance of the collection, defined in section 3.2.3.1 σ(x) – instance containing a grouping property that represents a node x, defined in section 6.2.2
1.2.3 Document Conventions Keywords defined by this specification use this monospaced font. Some sections of this specification are illustrated with non-normative examples. Example 1: text describing an example uses this paragraph style Non-normative examples use this paragraph style.
All examples in this document are non-normative and informative only. Examples labeled with ⚠ contain advanced concepts or make use of keywords that are defined only later in the text, they can be skipped at first reading. All other text is normative unless otherwise labeled. Paragraphs labeled 🚧 in this version of the specification contain restrictions that were not made in [OData-Data-Aggv4.0] OASIS Committee Specification 03. Also, some sections of [OData-Data-Agg-v4.0] OASIS Committee Specification 03 are omitted from this version. In later OASIS standard versions these restrictions may be lifted again and the omitted sections reintroduced. The ABNF rules [OData-ABNF] have been simplified in this version to reflect these restrictions. Also, some members of the OData Aggregation Vocabulary [OData-VocAggr] have been omitted from this version. These members are referenced by [OData-Data-Agg-v4.0] OASIS Committee Specification 03 but not by this version.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 7 of 69
Standards Track Work Product
2 Overview Open Data Protocol (OData) services expose a data model that describes the schema of the service in terms of the Entity Data Model (EDM, see [OData-CSDL]) and then allows for querying data in terms of this model. The responses returned by an OData service are based on that data model and retain the relationships between the entities in the model. Extending the OData query features with simple aggregation capabilities avoids cluttering OData services with an exponential number of explicitly modeled “aggregation level entities” or else restricting the consumer to a small subset of predefined aggregations. Adding the notion of aggregation to OData without changing any of the base principles in OData has two aspects: 1. Means for the consumer to query aggregated data on top of any given data model (for sufficiently capable data providers) 2. Means for the provider to annotate what data can be aggregated, and in which way, allowing consumers to avoid asking questions that the provider cannot answer Implementing any of these two aspects is valuable in itself independent of the other, and implementing both provides additional value for consumers. The provided aggregation annotations help a consumer understand more of the data structure looking at the service’s exposed data model. The query extensions allow the consumers to explicitly express the desired aggregation behavior for a particular query. They also allow consumers to formulate queries that utilize the aggregation annotations.
2.1 Example Data Model Example 2: The following diagram depicts a simple model that is used throughout this document.
Time
Category
Date: Edm.Date {id} Month: Edm.String Quarter: Edm.String Year: Edm.Int16
ID: Edm.String {id} Name: Edm.String
1 Category
1 Time
* Products
Customer ID: Edm.String {id} Name: Edm.String Country: Edm.String
1 Customer
*
Sale
* ID: Edm.String {id} Sales Amount: Edm.Decimal
1 Product * Sales
*
Product ID: Edm.String {id} Name: Edm.String Color: Edm.String TaxRate: Edm.Decimal
FoodProduct
SalesOrganization 1
Rating: Edm.Byte
SalesOrganization ID: Edm.String {id} Name: Edm.String
0..1 Superordinate
*
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
NonFoodProduct RatingClass: Edm.String
18 November 2025 - Page 8 of 69
Standards Track Work Product
The Amount property in the Sale entity type is an aggregatable property, and the properties of the related entity types are groupable. These can be arranged in hierarchies, for example: Product hierarchy based on groupable properties of the Category and Product entity types Customer hierarchy based on Country and Customer Time hierarchy based on Year, Month, and Date SalesOrganization hierarchy based on the recursive association to itself In the context of Online Analytical Processing (OLAP), this model might be described in terms of a Sales “cube” with an Amount “measure” and three “dimensions”. This document will avoid such terms, as they are heavily overloaded.
Query extensions and descriptive annotations can be applied to normalized schemas as well as partly or fully denormalized schemas. Example 3: The following diagram depicts a denormalized schema for the simple model. Sale Sales Category
ID: Edm.String {id} Amount: Edm.Decimal CategoryID: Edm.String CategoryName: Edm.String ProductID: Edm.String
Product
ProductName: Edm.String ProductColor: Edm.String ProductTaxRate: Edm.Decimal
Food Non-Food
FoodProductRating: Edm.Byte NonFoodProductRatingClass: Edm.String SalesOrganizationID: Edm.String
Sales Organization
SalesOrganizationName: Edm.String SalesOrganizationSuperordinateID: Edm.String TimeDate: Edm.Date
Time
TimeMonth: Edm.String TimeQuarter: Edm.String TimeYear: Edm.Int16 CustomerID: Edm.String
Customer
CustomerName: Edm.String CustomerCountry: Edm.String
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 9 of 69
Standards Track Work Product
2.2 Example Data Example 4: The following entity sets and sample data will be used to further illustrate the capabilities introduced by this extension. Products
Food
Non-Food
ID
Category
Name
Color
TaxRate
Rating
P1
PG1
Sugar
White
0.06
5
P2
PG1
Coffee
Brown
0.06
P3
PG2
Paper
White
0.14
n/a
P4
PG2
Pencil
Black
0.14
n/a
Time
RatingClass n/a n/a average
Categories
Date
Month
Quarter
Year
ID
Name
2022-01-01
2022-01
2022-1
2022
PG1
Food
2022-04-01
2022-04
2022-2
2022
PG2
Non-Food
2022-04-10
2022-04
2022-2
2022
Sales Organizations
…
ID
Customers
Superordinate
Sales
Name Corporate Sales
ID
Name
Country
US
Sales
US
C1
Joe
USA
US West
US
US West
C2
Sue
USA
US East
US
US East
C3
Sue
Netherlands
EMEA
Sales
EMEA
C4
Luc
France
EMEA Central
EMEA
EMEA Central
Sales Amount
Legend
ID
Customer
Time
Product
Sales Organization
1
C1
2022-01-03
P3
US West
1
Property
2
C1
2022-04-10
P1
US West
2
Key
3
C1
2022-08-07
P2
US West
4
Navigation Property
4
C2
2022-01-03
P2
US East
8
5
C2
2022-11-09
P3
US East
4
6
C3
2022-04-01
P1
EMEA Central
2
7
C3
2022-08-06
P3
EMEA Central
1
8
C3
2022-11-22
P3
EMEA Central
2
2.3 Example Use Cases Example 5: In the example model, one prominent use case is the relation of customers to products. The first question that is likely to be asked is: “Which customers bought which products?” This leads to the second more quantitative question: “Who bought how much of what?” The answer to the second question typically is visualized as a cross-table: Food
Non-Food Sugar
Coffee
14
2
12
5
5
Joe
6
2
4
1
1
Sue
8
8
4
4
USA
Netherlands Sue
Paper
2
2
3
3
2
2
3
3
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 10 of 69
Standards Track Work Product
The data in this cross-table can be written down in a shape that more closely resembles the structure of the data model, leaving cells empty that have been aggregated away: Customer/Country
Customer/Name
Product/Category/Name
Product/Name
USA
Joe
Non-Food
Paper
Amount 1
USA
Joe
Food
Sugar
2
USA
Joe
Food
Coffee
4
USA
Sue
Food
Coffee
8
USA
Sue
Non-Food
Paper
4
Netherlands
Sue
Food
Sugar
2
Netherlands
Sue
Non-Food
Paper
3
USA
Food
Sugar
2
USA
Food
Coffee
12
USA
Non-Food
Paper
5
Netherlands
Food
Sugar
2
Netherlands
Non-Food
Paper
3
USA
Joe
Food
6
USA
Joe
Non-Food
1
USA
Sue
Food
8
USA
Sue
Non-Food
4
Netherlands
Sue
Food
2
Netherlands
Sue
Non-Food
3
USA
Food
14
USA
Non-Food
5
Netherlands
Food
2
Netherlands
Non-Food
3
Note that this result contains seven fully qualified aggregate values, followed by fifteen rollup rows with subtotal values.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 11 of 69
Standards Track Work Product
3 System Query Option $apply A set transformation (transformation for short) is an operation on an input set that produces an output set. A transformation sequence is a sequence of set transformations, separated by forward slashes to express that they are consecutively applied. A transformation sequence may be invoked using the system query option $apply. The input set of the first set transformation is the collection addressed by the resource path. The output set of each set transformation is the input set for the next set transformation. The output set of the last set transformation in the transformation sequence invoked by the system query option $apply is the result of $apply. This is consistent with the use of service-defined bound and composable functions in path segments. Set transformations may also appear as a parameter of certain other set transformations defined below. The system query option $apply MUST NOT be used if the resource path addresses a single instance. The system query option $apply is evaluated first, then the other system query options are evaluated, if applicable, on the result of $apply, see [OData-Protocol, section 11.2.1]. Stability across requests for system query options $top and $skip [OData-Protocol, section 11.2.6.3] is defined in section 3.3.7. Each set transformation: carries over the input type to the output set such that it fits into the data model of the service. can mark certain navigation properties and stream properties for expansion by default, that is, they are expanded in the result of $apply in the absence of an $expand query option. may produce an output set with a different number of instances than the input set. does not necessarily guarantee that all properties of the instances in the output set have a well-defined value. Instances of an output set can contain structural and navigation properties, which can be declared or dynamic, as well as instance annotations. The allowed set transformations are defined in this section as well as in the section on Hierarchical Transformations. Service-defined bound functions that take a collection of instances of a structured type as their binding parameter and return a collection of instances of a structured type MAY be used as set transformations within $apply. Further transformations can follow the bound function. The parameter syntax for bound function segments is identical to the parameter syntax for bound functions in resource path segments or $filter expressions. See section 7.7 for an example. Parameter aliases [OData-URL, section 5.3] can be used inside the value of $apply wherever the ABNF rule applyTrafo [OData-ABNF] is reduced to a commonExpr [OData-URL, section 5.1.1] or a collectionExpr (section 3.6). If a data service that supports $apply does not support it on the collection identified by the request resource path, it MUST fail with 501 Not Implemented and a meaningful human-readable error message. On resource paths ending in /$count the system query option $apply is evaluated on the set identified by the resource path without the /$count segment, the result is the plain-text number of items in the result of $apply. This is similar to the combination of /$count and $filter. During serialization of the result of $apply declared properties and dynamic properties are represented as defined by the response format. Other properties have been aggregated away and are not represented in the response. The entities returned in the request examples in the following sections that involve aggregation are therefore transient.
3.1 Fundamentals of Input and Output Sets The definitions of italicized terms made in this section are used throughout this text, always with a hyperlink to this section.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 12 of 69
Standards Track Work Product
3.1.1 Type, Structure and Context URL All input sets and output sets in one transformation sequence are collections of the input type, that is the entity type or complex type of the first input set, or in other words, of the resource to which the transformation sequence is applied. The input type is determined by the entity model element identified within the metadata document by the context URL of that resource [OData-Protocol, section 10]. Individual instances in an input or output set can have a subtype of the input type. (See example 65.) The transformation sequence given as the $apply system query option is applied to the resource addressed by the resource path. The transformations defined below can have nested transformation sequences as parameters, these are then applied to resources that can differ from the current input set. The structure of an instance that occurs in an input or output set is defined by the names of the structural and navigation properties that the instance contains. Instances of an input type can have different structures, subject to the following rules: Declared properties of the input type or a nested or related type thereof or of a subtype of one of these MUST have their declared type and meaning when they occur in an input or output set. Single- or collection-valued primitive properties addressed by a property path starting at a non-transient entity MUST keep their values from the addressed resource path collection throughout the transformation sequence. Likewise, single- or collection-valued navigation property paths starting at a non-transient entity MUST keep addressing the same non-transient entities as in the addressed resource path collection. Instances in an output set need not have all declared or dynamic properties that occurred in the input set. Instances in an output set can have dynamic properties that did not occur in the input set. The name for such a dynamic property is called an alias, it is a simple identifier (see [OData-CSDL, section 15.2]). Aliases MUST differ from names of declared properties in the input type, from names of properties in the first input set, and from names of properties in the current input set. Aliases in one collection MUST also differ from each other. Instances in an output set that have all key properties of an entity also have the metadata associated with that entity, such as entity-id, read and edit URL (defined in [OData-Protocol, section 4]) and ETag (defined in [ODataProtocol, section 11.4.1.2]) as well as relations to other entities [OData-Protocol, section 11.2.7]. Here is an overview of the structural changes made by different transformations: During aggregation, many instances are replaced by one instance, properties that represent the aggregation level are retained, and others are replaced by dynamic properties holding the aggregate value of the many instances or a transformed copy of them. During compute, dynamic properties are added to each instance. During join, one instance with a collection of related instances is replaced by many copies, each of which is related via a dynamic property to one of the related instances. During concatenation, the same instances are transformed multiple times and the output sets with their potentially different structures are concatenated. An output set thus consists of instances with different structures. This is the same situation as with a collection of an open type ([OData-CSDL, section 6.3] and [OData-CSDL, section 9.3]) and it is handled in the same way. If the first input set is a collection of entities from a given entity set, then so are all input sets and output sets in the transformation sequence. The {select-list} in the context URL [OData-Protocol, section 10] MUST describe only properties that are present or annotated as absent (for example, if Core.Permissions is None [OData-Protocol, section 11.2.2]) in all instances of the collection, after applying any $select and $expand system query options. The {select-list} SHOULD describe as many such properties as possible, even if the request involves a concatenation that leads to a non-homogeneous structure. If the server cannot determine any such properties, the {select-list} MUST consist of just the instance annotation AnyStructure defined in the Core vocabulary. (See example 66.)
3.1.2 Sameness and Order Input sets and output sets are not sets of instances in the mathematical sense but collections, because the same instance can occur multiple times in them. In other words: A collection contains values (which can be instances of structured types or primitive values), possibly with repetitions. The occurrences of the values in the collection form a set odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 13 of 69
Standards Track Work Product
in the mathematical sense. The cardinality of a collection is the total number of occurrences in it. When this text describes a transformation algorithmically and stipulates that certain steps are carried out for each occurrence in a collection, this means that the steps are carried out multiple times for the same value if it occurs multiple times in the collection. A collection addressed by the resource path is returned by the service either as an ordered collection [OData-Protocol, section 11.4.9] or as an unordered collection. The same applies to collections that are nested in or related to the addressed resource as well as to collections that are the result of evaluating an expression starting with $root, which occur, for example, as the first parameter of a hierarchical transformation. But when such a collection is transformed by the $apply system query option, additional cases can arise that are neither ordered nor totally unordered. For example, the groupby transformation retains any order within a group but not between groups. ⚠ Example 6: Request the top 10 sales per customer. The processing of the request can be parallelized per customer and the responses per customer can be interleaved in the overall response. This means that for any given customer, their top 10 sales appear in the desired order, though not consecutively. GET /service/Sales?$apply=groupby((Customer),orderby(Amount desc)/top(10))
For every transformation defined in the following sections, it will be specified how it orders its output set, based on the order of its input set. The order of the last output set can be further influenced by a $orderby system query option before it is observed in the response payload. An order of a collection is more precisely defined as follows: Given two different occurrences u1 and u2 in a collection, which may be of the same value or of different values, u1 precedes u2 or u2 precedes u1, but not both. It can be neither, in which case the relative order of u1 and u2 does not matter. If u1 precedes u2 and u2 precedes u3, then u1 also precedes u3, and u1 never precedes u1. (This is a partial order in the mathematical sense defined on the set of occurrences.) When transformations are defined in the following sections, the algorithmic description sometimes contains an orderpreserving loop over a collection. Such a loop processes the occurrences in an order chosen by the service in such a way that u1 is processed before u2 whenever u1 precedes u2. Likewise, in an order-preserving sequence u1, … , un we have i < j whenever ui precedes uj. A collection can be stable-sorted by a list of expressions. In the stable-sorted collection an occurrence u1 precedes u2 if and only if either u1 precedes u2 according to the rules of [OData-Protocol, section 11.2.6.2] or these rules do not determine a precedence in either direction between u1 and u2 but u1 preceded u2 in the collection before the sort. Stable-sorting of an ordered collection produces another ordered collection. A stable-sort does not necessarily produce a total order, the sorted collection may still contain two occurrences whose relative order does not matter. The transformation orderby performs a stable-sort. The output set of a basic aggregation transformation can contain instances of an entity type without entity-id. After a concat transformation, different occurrences of the same entity can differ in individual non-declared properties. To account for such cases, the definition of sameness given in [OData-URL, section 5.1.1.1.1] is refined here. Instances of structured types are the same if both are instances of complex types and both are null or both have the same structure and same values with null considered different from absent or both are instances of entity types without entity-id (see [OData-Protocol, section 4.3]) and both are null or both have the same structure and same values with null considered different from absent (informally speaking, they are compared like complex instances) or (1) both are instances of the same entity type with the same entity-id (non-transient entities, see [OData-Protocol, section 4.1]) and (2) the structural and navigation properties contained in both have the same values (for nonodata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 14 of 69
Standards Track Work Product
primitive properties the sameness of values is decided by a recursive invocation of this definition). If this is fulfilled, the instances are called complementary representations of the same non-transient entity. If this case is encountered at some recursion level while the sameness of non-transient entities u1 and u2 is established, a merged representation of the entity u1 = u2 exists that contains all properties of u1 and u2. But if the instances both occur in the last output set, services MUST represent each with its own structure in the response payload. If the first condition is fulfilled but not the second, the instances are not the same and are called contradictory representations of the same non-transient entity. (Example 84 describes a use case for this.) Collections are the same if there is a one-to-one correspondence f between them such that corresponding occurrences are of the same value and an occurrence u1 precedes another occurrence u2 if and only if the occurrence f(u1) precedes the occurrence f(u2), where the occurrences u1 and u2 may be of the same value or of different values. (A one-to-one correspondence with this second property is called order-preserving.)
3.1.3 Evaluation of Data Aggregation Paths This document specifies how a data aggregation path that occurs in a request is evaluated by the service. If such an evaluation fails, the service MUST reject the request. For a data aggregation path to be a common expression according to [OData-URL, section 5.1.1], its segments must be single-valued with the possible exception of the last segment, and it can then be evaluated relative to an instance of a structured type. For the transformations defined in this document, a data aggregation path can also be evaluated relative to a collection A, even if it has arbitrary collection-valued segments itself. To this end, the following notation is used in the subsequent sections: If A is a collection and p a data aggregation path, optionally followed by a type-cast segment, the result of such a path evaluation is denoted by Γ(A, p) and defined as the unordered concatenation, possibly containing repetitions, of the collections γ(u, p) for each u in A that is not null. The function γ(u, p) takes a non-null value and a path as arguments and returns a collection of instances of structured types or primitive values, depending on the type of the final segment of p. It is recursively defined as follows: 1. If p is an empty path, let B be a collection with u as its single member and continue with step 9. 2. Let p1 be the first segment of p and p2 the remainder, if any, such that p equals the concatenated path p1/p2. 3. If p1 is a type-cast segment and u is of its type or a subtype thereof, let v = u and continue with step 8. 4. If p1 is a type-cast segment and u is not of its type or a subtype thereof, let B be an empty collection and continue with step 9. (This rule follows [OData-URL, section 4.11] rather than [OData-CSDL, section 14.4.1.1].) 5. Otherwise, p1 is a non-type-cast segment. If u does not contain a structural or navigation property p1, let B be an empty collection and continue with step 9. 6. If p1 is single-valued, let v be the value of the structural or navigation property p1 in u. If v is null, let B be an empty collection and continue with step 9; otherwise continue with step 8. 7. Otherwise, p1 is collection-valued. Let C be the collection addressed by the structural or navigation property p1 in u, and let B = Γ(C, p2). Then continue with step 9. 8. Let B = γ(v, p2). 9. Return B. This notation is extended to the case of an empty path e by setting Γ(A, e) = A with null values removed. Note the collections returned by Γ and γ never contain the null value. Also, every instance u in Γ(A, p) occurs also in A or nested into A, therefore an algorithmic step like “Add a dynamic property to each u in Γ(A, p)” effectively changes A.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 15 of 69
Standards Track Work Product
3.2 Basic Aggregation 3.2.1 Transformation aggregate 3.2.1.1 Aggregation Algorithm The aggregate transformation takes a comma-separated list of one or more aggregate expressions as parameters and returns an output set with a single instance of the input type without entity-id containing one property per aggregate expression, representing the aggregated value of the input set. An aggregate expression MUST have one of the types listed below. To compute the value of the property for a given aggregate expression, the aggregate transformation first determines a collection A of instances of structured types or primitive values, based on the input set of the aggregate transformation, and a path p that occurs in the aggregate expression. Let p1 denote a data aggregation path with single- or collection-valued segments and p2 a type-cast segment. Depending on its type, the aggregate expression contains a path p = p1 or p = p2 or p = p1/p2. Each type of aggregate expression defines a function f(A) which the aggregate transformation evaluates to obtain the property value. The property is a dynamic property, except for a special case in type 4. In types 1 and 2, the aggregate expression MUST end with the keyword with and an aggregation method g. The aggregation method also determines the type of the dynamic property. In types 1, 2, and 3 the aggregate expression MUST, and in type 4 it MAY, be followed by the keyword as and an alias, which is then the name of the dynamic property. Types of aggregate expressions: 1. A path p = p1 or p = p1/p2 where the last segment of p1 has a complex or entity or aggregatable primitive type whose values can be aggregated using the specified aggregation method g, or p = p2 if the input set can be aggregated using the custom aggregation method g. Let f(A) = g(A). 2. An aggregatable expression whose values can be aggregated using the specified aggregation method g. Let f(A) = g(B) where B is the collection consisting of the values of the aggregatable expression evaluated relative to each occurrence in A with null values removed from B. In this type, p is absent. 3. A path p/$count (see section 3.2.1.4) with optional prefix p/ where p = p1 or p = p2 or p = p1/p2. Let f(A) be the cardinality of A. 4. A path p/c consisting of an optional prefix p/ with p = p1 or p = p1/p2 where the last segment of p1 has a structured type or p = p2, and a custom aggregate c defined on the collection addressed by p. Let f(A) = c(A). If computation of the custom aggregate fails, the service MUST reject the request. In the absence of an alias: The name of the property is the name of the custom aggregate. The property is a dynamic property whose type is determined by the custom aggregate, unless there is a declared property with that name. The latter case is allowed by the CustomAggregate annotation. Determination of A: Let I be the input set. If p is absent, let A = I with null values removed. Otherwise, let q be the portion of p up to and including the last navigation property, if any, and any type-cast segment that immediately follows, and let r be the remainder, if any, of p that contains no navigation properties, such that p equals the concatenated path q / r. The aggregate transformation considers each entity reached via the path q exactly once. To this end, using the Γ notation: If q is non-empty, let E = Γ(I, q) and remove duplicates from that entity collection: If multiple representations of the same non-transient entity are reached, the service MUST merge them into one occurrence in E if they are complementary and MUST reject the request if they are contradictory. If multiple occurrences of the same transient entity are reached, the service MUST keep only one occurrence in E. If q is empty, let E = I .
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 16 of 69
Standards Track Work Product
Then, if r is empty, let A = E, otherwise let A = Γ(E, r), this consists of instances of structured types or primitive values, possibly with repetitions. 3.2.1.2 Keyword as Aggregate expressions can be followed by the as keyword followed by an alias. Example 7: GET /service/Sales?$apply=aggregate(Amount with sum as Total, Amount with max as MxA) results in { "@context": "$metadata#Sales(Total, MxA)", "value": [ { "Total@type": "Decimal", "Total": 24, "MxA@type": "Decimal", "MxA": 8 } ] } Example 8: GET /service/Sales?$apply=aggregate(Amount mul Product/TaxRate with sum as Tax) results in { "@context": "$metadata#Sales(Tax)", "value": [ { "Tax@type": "Decimal", "Tax": 2.08 } ] }
An alias affects the structure of the output set: each alias corresponds to a dynamic property in a $select option. 3.2.1.3 Aggregation Methods Values can be aggregated using the standard aggregation methods sum, min, max, average, and countdistinct, or with custom aggregation methods defined by the service. Only types 1 and 2 of the aggregation algorithm involve aggregation methods, and the algorithm ensures that no null values occur among the values to be aggregated. 3.2.1.3.1 Standard Aggregation Method sum
The standard aggregation method sum can be applied to numeric values to return the sum of the values, or null if there are no values to be aggregated. The provider MUST choose a single type for the property across all instances of that type in the result that is capable of representing the aggregated values. This may require a larger integer type, Edm.Decimal with sufficient Precision and Scale, or Edm.Double. Example 9: GET /service/Sales?$apply=aggregate(Amount with sum as Total) results in { "@context": "$metadata#Sales(Total)", "value": [ { "Total@type": "Decimal", "Total": 24 }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 17 of 69
Standards Track Work Product
] }
3.2.1.3.2 Standard Aggregation Method min
The standard aggregation method min can be applied to values with a totally ordered domain to return the smallest of the values, or null if there are no values to be aggregated. The result property will have the same type as the input property. Example 10: GET /service/Sales?$apply=aggregate(Amount with min as MinAmount) results in { "@context": "$metadata#Sales(MinAmount)", "value": [ { "MinAmount@type": "Decimal", "MinAmount": 1 } ] }
3.2.1.3.3 Standard Aggregation Method max
The standard aggregation method max can be applied to values with a totally ordered domain to return the largest of the values, or null if there are no values to be aggregated. The result property will have the same type as the input property. Example 11: GET /service/Sales?$apply=aggregate(Amount with max as MaxAmount) results in { "@context": "$metadata#Sales(MaxAmount)", "value": [ { "MaxAmount@type": "Decimal", "MaxAmount": 8 } ] }
3.2.1.3.4 Standard Aggregation Method average
The standard aggregation method average can be applied to numeric values to return the sum of the values divided by the count of the values, or null if there are no values to be aggregated. The provider MUST choose a single type for the property across all instances of that type in the result that is capable of representing the aggregated values; either Edm.Double or Edm.Decimal with sufficient Precision and Scale. Example 12: GET /service/Sales?$apply=aggregate(Amount with average as AverageAmount) results in { "@context": "$metadata#Sales(AverageAmount)", "value": [ { "AverageAmount@type": "Decimal", "AverageAmount": 3.0 }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 18 of 69
Standards Track Work Product
] }
3.2.1.3.5 Standard Aggregation Method countdistinct
The aggregation method countdistinct can be applied to arbitrary collections to count the distinct values. Instance comparison uses the definition of equality in [OData-URL, section 5.1.1.1.1]. The result property MUST have type Edm.Decimal with Scale 0 and sufficient Precision. Example 13: GET /service/Sales?$apply=aggregate(Product with countdistinct as DistinctProducts) results in { "@context": "$metadata#Sales(DistinctProducts)", "value": [ { "DistinctProducts@type": "Decimal", "DistinctProducts": 3 } ] }
The number of instances in the input set can be counted with the aggregate expression $count. 3.2.1.3.6 Custom Aggregation Methods
Services can define custom aggregation methods if the functionality offered by the standard aggregation methods is not sufficient for the intended consumers. Custom aggregation methods MUST use a namespace-qualified name (see [OData-ABNF]), i.e. contain at least one dot. Dot-less names are reserved for future versions of this specification. ⚠ Example 14: custom aggregation method that concatenates distinct string values separated by commas GET /service/Sales?$apply=groupby((Customer/Country), aggregate(Amount with sum as Total, Product/Name with Custom.concat as ProductNames)) results in { "@context": "$metadata#Sales(Customer(Country),Total,ProductNames)", "value": [ { "Customer": { "Country": "Netherlands" }, "Total@type": "Decimal", "Total": 5, "ProductNames": "Paper,Sugar" }, { "Customer": { "Country": "USA" }, "Total@type": "Decimal", "Total": 19, "ProductNames": "Coffee,Paper,Sugar" } ] }
3.2.1.4 Aggregate Expression $count The aggregate expression $count is defined as type 3 in the aggregation algorithm. It MUST always specify an alias and MUST NOT specify an aggregation method. The result property MUST have type Edm.Decimal with Scale 0 and sufficient Precision. Example 15:
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 19 of 69
Standards Track Work Product
GET /service/Sales?$apply=aggregate($count as SalesCount) results in { "@context": "$metadata#Sales(SalesCount)", "value": [ { "SalesCount@type": "Decimal", "SalesCount": 8 } ] }
3.2.2 Transformation concat The concat transformation takes two or more parameters, each of which is a sequence of set transformations. It applies each transformation sequence to the input set and concatenates the intermediate output sets in the order of the parameters into the output set, preserving the ordering of the individual output sets as well as the structure of each instance in these sets, potentially leading to a non-homogeneously structured output set. If different intermediate output sets contain dynamic properties with the same alias, clients SHOULD ensure they have the same type and meaning in each intermediate output set. ⚠ Example 16: GET /service/Sales?$apply=concat(topcount(2,Amount), aggregate(Amount)) results in { "@context": "$metadata#Sales(Amount)", "value": [ { "ID": 4, "Amount": 8 }, { "ID": 3, "Amount": 4 }, { "Amount": 24 } ] } Note that two Sales entities with the second highest amount 4 exist in the input set; the entity with ID 3 is included in the result, because the service chose to use the ID property for imposing a stable ordering.
3.2.3 Transformation groupby The groupby transformation takes one or two parameters where the second is a list of set transformations, separated by forward slashes to express that they are consecutively applied. If the second parameter is not specified, it defaults to a single transformation whose output set consists of a single instance of the input type without properties and without entity-id. The groupby transformation partitions the input set by the values of certain “grouping properties” and applies the given set transformations to each partition, this is called “simple grouping”. 3.2.3.1 Simple Grouping The first parameter of groupby specifies the grouping properties, a comma-separated parenthesized list G of one or more data aggregation paths with single-valued segments. The same path SHOULD NOT appear more than once; redundant property paths MAY be considered valid, but MUST NOT alter the meaning of the request. Navigation properties and stream properties specified in grouping properties are expanded by default (see example 63). The algorithmic description of this transformation makes use of the following definitions: Let u[q] denote the value of a structural or navigation property q in an instance u. A path p1 is called a prefix of a path p if there is a non-empty path p2 such that p equals the concatenated path p1/p2. Let e denote the empty path.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 20 of 69
Standards Track Work Product
The output set of the groupby transformation is constructed in five steps. 1. For each occurrence u in the input set, a projection is computed that contains only the grouping properties. This projection is sG(u, e) and the function sG(u, p) takes an instance and a path relative to the input set as arguments and is computed recursively as follows: Let v be an instance of the type of u without properties and without entity-id. For each structural or navigation property q of u: If u has a subtype of the type addressed by p and q is only declared on that subtype, let p′ = p/p′′/q where p′′ is a type-cast to the subtype, otherwise let p′ = p/q. If p′ occurs in G, let v[q] = u[q]. Otherwise, if p′ is a prefix of a path in G and u[q] has a structured type, let v[q] = sG(u[q], p′). Return v. 2. The input set is split into subsets where two instances are in the same subset if their projections are the same. If representations of the same non-transient entity are encountered during the comparison of two projections, the service MUST assign them to one subset with the merged representation if they are complementary and MUST reject the request if they are contradictory. 3. The set transformations from the second parameter are applied to each subset, resulting in a new set of potentially different structure and cardinality. Associated with each resulting set is the common projection of the instances in the subset from which the resulting set was computed. 4. Each set resulting from the previous step is transformed to contain the associated common projection s. This transformation is denoted by ΠG(s) and is defined below. 5. The output set is the concatenation of the transformed sets from the previous step. The order of occurrences from the same transformed set remains the same, and no order is defined between occurrences from different transformed sets. Definition of ΠG(s): Prerequisites: G is a list of data aggregation paths and s is an instance of the input type. The output set of the transformation ΠG(s) is in one-to-one correspondence with its input set via the order-preserving mapping u ↦ aG(u, s, e). The function aG(u, s, p) takes two instances and a path relative to the input set as arguments and is computed recursively as follows: 1. If necessary, cast u to a subtype so that its type contains all structural and navigation properties of s. 2. For each structural or navigation property q of s: If s has a subtype of the type addressed by p and q is only declared on that subtype, let p′ = p/p′′/q where p′′ is a type-cast to the subtype, otherwise let p′ = p/q. If q is a single-valued primitive structural property or p′ occurs in G, let u[q] = s[q]. (In the case where p′ occurs in G we also call q a final segment from G.) Otherwise, if q is single-valued, let u[q] = aG(u[q], s[q], p′). Otherwise, the behavior is undefined. (Such cases never occur when ΠG(s) is used in this document.) 3. Return u. Example 17: GET /service/Sales?$apply=groupby((Customer/Country,Product/Name), aggregate(Amount with sum as Total)) results in { "@context": "$metadata#Sales(Customer(Country),Product(Name),Total)", "value": [ { "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 3 },
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 21 of 69
Standards Track Work Product
{ "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 2 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 5 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 2 } ] }
If the second parameter is omitted, steps 2 and 3 above produce one instance containing only the grouping properties per distinct value combination. ⚠ Example 18: GET /service/Sales?$apply=groupby((Product/Name,Amount)) results in { "@context": "$metadata#Sales(Product(Name),Amount)", "value": [ { "Product": { "Name": "Coffee" }, "Amount": 4 }, { "Product": { "Name": "Coffee" }, "Amount": 8 }, { "Product": { "Name": "Paper" }, "Amount": 1 }, { "Product": { "Name": "Paper" }, "Amount": 2 }, { "Product": { "Name": "Paper" }, "Amount": 4 }, { "Product": { "Name": "Sugar" }, "Amount": 2 } ] } Note that the result has the same structure, but not the same content as GET /service/Sales?$expand=Product($select=Name)&$select=Amount
A groupby transformation affects the structure of the output set similar to $select where each grouping property corresponds to an item in a $select clause.
3.3 Transformations Producing a Subset These transformations produce an output set that is a subset of their input set, possibly in a different order. Some of the algorithmic descriptions below make use of the following definition: A total order of a collection is called stable across requests if it is the same for all requests that construct the collection by executing the same resource path and transformations, possibly nested, on the same underlying data. ⚠ Example 19: A stable total order is required for the input set of a skip transformation. The following request constructs that input set by executing the groupby transformation on the Sales entity collection, computing the total sales per customer. Because of the subsequent skip transformation, the service must endow this with a stable total order. Then the request divides the total sales per customer into pages of N customers and returns page number i in a reproducible manner (as long as the underlying data do not change). GET /service/Sales?$apply= groupby((Customer),aggregate(Amount with sum as Total)) /skip(M)/top(N) where the number in skip is M = (i − 1) ⋅ N . Other values of M can be used to skip, for example, half a page.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 22 of 69
Standards Track Work Product
3.3.1 Top/bottom transformations These transformations take two parameters. The first parameter MUST be an expression that is evaluable on the input set as a collection, without reference to an individual instance (and which therefore cannot be a property path). The second parameter MUST be an expression that is evaluated on each instance of the input set in turn. The output set is constructed as follows: 1. Let A be a copy of the input set with a total order that is chosen by the service (it need not preserve any existing order). The total order MUST be stable across requests. (This is the order of the eventual output set of this transformation.) 2. Let B be a copy of A that is stable-sorted in ascending (for transformations starting with bottom) or descending (for transformations starting with top) order of the value specified in the second parameter. (This is the order in which contributions to the output set are considered.) 3. Start with an empty output set. 4. Loop over B in its total order. 5. Exit the loop if a condition is met. This condition depends on the transformation being executed and is given in the subsections below. 6. Insert the current item of the loop into the output set in the order of A. 7. Continue the loop. For example, if the input set consists of non-transient entities and the datastore contains an index ordered by the second parameter and then the entity-id, a service may implement this algorithm with A = B ordered like this index. The order of the output set can be influenced with a subsequent orderby transformation. 3.3.1.1 Transformations bottomcount and topcount The first parameter MUST evaluate to a positive integer c. The second parameter MUST evaluate to a primitive type whose values are totally ordered. In step 5, exit the loop if the cardinality of the output set equals c. Example 20: GET /service/Sales?$apply=bottomcount(2,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 1, "Amount": 1 }, { "ID": 7, "Amount": 1 } ] } Example 21: GET /service/Sales?$apply=topcount(2,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 } ] }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 23 of 69
Standards Track Work Product
Note that two Sales entities with the second highest amount 4 exist in the input set; the entity with ID 3 is included in the result, because the service chose to use the ID property for imposing a stable ordering in step 1. Such a logic needs to be in place even with a preceding orderby since it cannot be ensured that it creates a stable order of the instances on the expressions of the second parameter.
3.3.1.2 Transformations bottompercent and toppercent The first parameter MUST evaluate to a positive number p less than or equal to 100. The second parameter MUST evaluate to a number. In step 5, exit the loop if the ratio of the sum of the numbers addressed by the second parameter in the output set to their sum in the input set equals or exceeds p percent. Example 22: GET /service/Sales?$apply=bottompercent(50,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 1, "Amount": 1 }, { "ID": 2, "Amount": 2 }, { "ID": 5, "Amount": 4 }, { "ID": 6, "Amount": 2 }, { "ID": 7, "Amount": 1 }, { "ID": 8, "Amount": 2 } ] } Example 23: GET /service/Sales?$apply=toppercent(50,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 } ] }
3.3.1.3 Transformations bottomsum and topsum The first parameter MUST evaluate to a number s. The second parameter MUST be an aggregatable expression that evaluates to a number. In step 5, exit the loop if the sum of the numbers addressed by the second parameter in the output set is greater than or equal to s. Example 24: GET /service/Sales?$apply=bottomsum(7,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 1, "Amount": 1 }, { "ID": 2, "Amount": 2 }, { "ID": 6, "Amount": 2 }, { "ID": 7, "Amount": 1 }, { "ID": 8, "Amount": 2 }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 24 of 69
Standards Track Work Product
] } Example 25: GET /service/Sales?$apply=topsum(15,Amount) results in { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 }, { "ID": 5, "Amount": 4 } ] }
3.3.2 Transformation filter The filter transformation takes a Boolean expression that could also be passed as a $filter system query option. Its output set is the subset of the input set containing all instances (possibly with repetitions) for which this expression, evaluated relative to the instance, yields true. No order is defined on the output set. Example 26: GET /service/Sales?$apply=filter(Amount gt 3) results in { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 }, { "ID": 5, "Amount": 4 } ] }
3.3.3 Transformation orderby The orderby transformation takes a list of expressions that could also be passed as a $orderby system query option. Its output set consists of the instances of the input set in the same order $orderby would produce for the given expressions, but keeping the relative order from the input set if the given expressions do not distinguish between two instances. The orderby transformation thereby performs a stable-sort. A service supporting this transformation MUST at least offer sorting by values addressed by property paths, including dynamic properties, with both suffixes asc and desc. Example 27: GET /service/Sales?$apply=groupby((Product/Name), aggregate(Amount with sum as Total)) /orderby(Total desc) results in { "@context": "$metadata#Sales(Product(Name),Total)", "value": [ { "Product": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Product": { "Name": "Paper" }, odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 25 of 69
Standards Track Work Product
"Total@type": "Decimal", "Total": { "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total":
8 }, 4 }
] }
3.3.4 Transformation search The search transformation takes a search expression that could also be passed as a $search system query option. Its output set is the subset of the input set containing all instances (possibly with repetitions) that match this search expression. Closing parentheses in search expressions must be within single or double quotes in order to avoid syntax errors like search()). No order is defined on the output set. Example 28: assuming that free-text search on Sales takes the related product name into account, GET /service/Sales?$apply=search(coffee) results in { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 } ] }
3.3.5 Transformation skip The skip transformation takes a non-negative integer c as argument. Let A be a copy of the input set with a total order that extends any existing order of the input set but is otherwise chosen by the service. The total order MUST be stable across requests. The transformation excludes from the output set the first c occurrences in A. It keeps all remaining instances in the same order as they occur in A. Example 29: GET /service/Sales?$apply=orderby(Customer/Name desc)/skip(2)/top(2) results in { "@context": "$metadata#Sales", "value": [ { "ID": 6, "Amount": 2 }, { "ID": 7, "Amount": 1 } ] }
3.3.6 Transformation top The top transformation takes a non-negative integer c as argument. Let A be a copy of the input set with a total order that extends any existing order of the input set but is otherwise chosen by the service. The total order MUST be stable across requests. If A contains more than c instances, the output set consists of the first c occurrences in A. Otherwise, the output set equals A. The instances in the output set are in the same order as they occur in A. Note the transformation top(0) produces an empty output set.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 26 of 69
Standards Track Work Product
Example 30: GET /service/Sales?$apply=orderby(Customer/Name desc)/top(2) results in { "@context": "$metadata#Sales", "value": [ { "ID": 4, "Amount": 8 }, { "ID": 5, "Amount": 4 } ] }
3.3.7 Stable Total Order Before $skip and $top When the system query options $top and $skip [OData-Protocol, section 11.2.6.3] are executed after the system query option $apply and after $filter and $orderby, if applicable, they operate on a collection with a total order that extends any existing order but is otherwise chosen by the service. The total order MUST be stable across requests.
3.4 One-to-One Transformations These transformations produce an output set in one-to-one correspondence with their input set. The output set is initially a clone of the input set, then dynamic properties are added to the output set. The values of properties copied from the input set are not changed, nor is the order of instances changed.
3.4.1 Transformation identity The output set of the identity transformation is its input set in unchanged order. Example 31: Add a grand total row to the Sales result set GET /service/Sales?$apply=concat(identity,aggregate(Amount with sum as Total))
3.4.2 Transformation compute The compute transformation takes a comma-separated list of one or more compute expressions as parameters. A compute expression is a common expression followed by the as keyword, followed by an alias. The output set is constructed by copying the instances of the input set and adding one dynamic property per compute expression to each occurrence in the output set. The name of each added dynamic property is the alias of the corresponding compute expression. The value of each added dynamic property is computed relative to the corresponding instance. Services MAY support expressions that address dynamic properties added by other expressions within the same compute transformation, provided that the service can determine an evaluation sequence. The type of the property is determined by the rules for evaluating common expressions and numeric promotion defined in [OData-URL, section 5.1.1]. Example 32: GET /service/Sales?$apply=compute(Amount mul Product/TaxRate as Tax) results in { "@context": "$metadata#Sales(*,Tax)", "value": [ { "ID": 1, "Amount": 1, "Tax@type": "Decimal", "Tax": 0.14 }, { "ID": 2, "Amount": 2, "Tax@type": "Decimal", "Tax": 0.12 }, { "ID": 3, "Amount": 4, "Tax@type": "Decimal", "Tax": 0.24 }, { "ID": 4, "Amount": 8, "Tax@type": "Decimal", "Tax": 0.48 }, odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 27 of 69
Standards Track Work Product
{ "ID": 5, "Amount": 4, "Tax@type": "Decimal", "Tax": 0.56 }, { "ID": 6, "Amount": 2, "Tax@type": "Decimal", "Tax": 0.12 }, { "ID": 7, "Amount": 1, "Tax@type": "Decimal", "Tax": 0.14 }, { "ID": 8, "Amount": 2, "Tax@type": "Decimal", "Tax": 0.28 } ] }
3.5 Transformations Changing the Input Set Structure The output set of the join transformations differs from their input set in the number of instances as well as in their structure, but reflects the order of the input set.
3.5.1 Transformations join and outerjoin The join and outerjoin transformations take as their first parameter p a collection-valued complex or navigation property, optionally followed by a type-cast segment to address only instances of that derived type or one of its subtypes, followed by the as keyword, followed by an alias. The optional second parameter specifies a transformation sequence T . For each occurrence u in an order-preserving loop over the input set 1. the instance collection A addressed by p is identified. 2. If T is provided, A is replaced with the result of applying T to A. 3. In case of an outerjoin, if A is empty, a null instance is added to it. 4. For each occurrence v in an order-preserving loop over A an instance w is appended to the output set of the transformation: The instance w is a clone of u with an additional dynamic property whose name is the given alias and whose value is v. The dynamic property is a navigation property if p is a collection-valued navigation property, otherwise it is a complex property. The dynamic property carries as control information the context URL of v. Example 33: all links between products and sales instances GET /service/Products?$apply=join(Sales as Sale)&$select=ID&$expand=Sale results in { "@context": "$metadata#Products(ID,Sale())", "value": [ { "ID": "P1", "Sale": { "@context": "#Sales/$entity", "ID": 2, "Amount": 2 } }, { "ID": "P1", "Sale": { "@context": "#Sales/$entity", "ID": 6, "Amount": 2 } }, { "ID": "P2", "Sale": { "@context": "#Sales/$entity", "ID": 3, "Amount": 4 } }, { "ID": "P2", "Sale": { "@context": "#Sales/$entity", "ID": 4, "Amount": 8 } }, { "ID": "P3", "Sale": { "@context": "#Sales/$entity", "ID": 1, "Amount": 1 } }, odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 28 of 69
Standards Track Work Product
{ "ID": "P3", "Sale": { "@context": "#Sales/$entity", "ID": 5, "Amount": 4 } }, { "ID": "P3", "Sale": { "@context": "#Sales/$entity", "ID": 7, "Amount": 1 } }, { "ID": "P3", "Sale": { "@context": "#Sales/$entity", "ID": 8, "Amount": 2 } } ] } In this example, $expand=Sale is used to include the target entities in the result. There are no subsequent transformations like groupby that would cause it to be expanded by default. If the first parameter Sales was a collection-valued complex property of type SalesModel.SalesComplexType, the complex property Sale would be in the result regardless, and its context would be "@context": "#SalesModel.SalesComplexType". Applying outerjoin instead would return an additional instance for product with "ID": "P4" and Sale having a null value.
3.6 Expressions Evaluable on a Collection The following two subsections introduce two new types of expression that are evaluated relative to a collection, called the input collection. These expressions are either prepended with a collection-valued path p followed by a forward slash, like a lambda operator [OData-URL, section 5.1.1.13]. The collection identified by that path is then the input collection for the expression. or prepended with the keyword $these followed by a forward slash, the input collection is then the current collection defined as follows: In a system query option other than $apply, possibly nested within $expand or $select, the current collection is the collection that is the subject of the system query option. In a path segment that addresses a subset of a collection [OData-URL, section 4.12], the current collection is the collection that is the subject of the path segment. In an $apply transformation, the current collection is the input set of the transformation.
3.6.1 Function aggregate The aggregate function allows the use of aggregated values in expressions. It takes a single parameter accepting an aggregate expression and returns the aggregated value of type Edm.PrimitiveType as the result from applying the aggregate expression on its input collection. More precisely, if α is an aggregate expression, the function p/aggregate(α) or $these/aggregate(α) evaluates to the value of the property D in the single instance of the output set that is produced when the transformation aggregate(α as D) is applied with the input collection as input set. Example 34: Sales making up at least a third of the total sales amount. GET /service/Sales?$filter=Amount mul 3 ge $these/aggregate(Amount with sum) results in { "@context": "$metadata#Sales", "value": [ { "ID": "4", "Amount": 8 }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 29 of 69
Standards Track Work Product
] } Example 35: Products with more than 1.00 sales tax. The aggregate expression of type 2 combines paths with and without $it prefix (compare this with example 8). GET /service/Products?$filter=Sales/aggregate(Amount mul $it/TaxRate with sum) gt 1
⚠ Example 36: products with a single sale of at least twice the average sales amount GET /service/Products?$filter=Sales/any(s:s/Amount ge Sales/aggregate(Amount with average) mul 2) Both examples result in { "@context": "$metadata#Products", "value": [ { "ID": "P3", "Name": "Paper", "Color": "White", "TaxRate": 0.14 } ] }
3.6.2 Expression $count The expression $count evaluates to the cardinality of the input collection. Example 37: The input collection for $count consists of all sales entities, the top third of sales entities by amount form the result. GET /service/Sales?$apply=topcount($these/$count div 3,Amount) results in 2 (a third of 8, rounded down) entities. (This differs from toppercent(33.3,Amount), which returns only the sales entity with ID 4, because that already makes up a third of the total amount.) { "@context": "$metadata#Sales", "value": [ { "ID": 3, "Amount": 4 }, { "ID": 4, "Amount": 8 } ] }
A definition that is equivalent to a $count expression after a collection-valued path was made in [OData-URL, section 4.8].
3.7 Function isdefined Properties that are not explicitly mentioned in aggregate or groupby are considered to have been aggregated away. Since they are treated as having the null value in $filter expressions [OData-URL, section 5.1.1.15], the $filter expression Product eq null cannot distinguish between an instance containing the value for the null product and the instance containing the aggregated value across all products (where the Product has been aggregated away). The function isdefined can be used to determine whether a property is present or absent in an instance. It takes a single-valued property path as its only parameter and returns true if the property is present in the instance for which the expression containing the isdefined function call is evaluated. A present property can still have the null value; it can represent a grouping of null values, or an aggregation that results in a null value. Example 38: Product has been aggregated away, causing an empty result GET /service/Sales?$apply=aggregate(Amount with sum as Total) &$filter=isdefined(Product)
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 30 of 69
Standards Track Work Product
results in { "@context": "$metadata#Sales(Total)", "value": [] }
3.8 Evaluating $apply as an Expand and Select Option The new system query option $apply can be used as an expand or select option to inline the result of aggregating related entities or nested instances. The rules for evaluating $apply are applied in the context of the related collection of entities or the selected collection of instances, meaning this context defines the input set of the first transformation. Furthermore, $apply is evaluated first, and other expand or select options on the same (navigation) property are evaluated on the result of $apply. Example 39: products with aggregated sales GET /service/Products ?$expand=Sales($apply=aggregate(Amount with sum as Total)) results in { "@context": "$metadata#Products(Sales(Total))", "value": [ { "ID": "P2", "Name": "Coffee", "Color": "Brown", "TaxRate": 0.06, "Sales": [ { "Total@type": "Decimal", "Total": 12 } ] }, { "ID": "P3", "Name": "Paper", "Color": "White", "TaxRate": 0.14, "Sales": [ { "Total@type": "Decimal", "Total": 8 } ] }, { "ID": "P4", "Name": "Pencil", "Color": "Black", "TaxRate": 0.14, "Sales": [ { "Total": null } ] }, { "ID": "P1", "Name": "Sugar", "Color": "White", "TaxRate": 0.06, "Sales": [ { "Total@type": "Decimal", "Total": 4 } ] } ] }
3.9 ABNF for Extended URL Conventions The normative ABNF construction rules for this specification are defined in [OData-Agg-ABNF]. They incrementally extend the rules defined in [OData-ABNF].
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 31 of 69
Standards Track Work Product
4 Cross-Joins and Aggregation OData supports querying related entities through defining navigation properties in the data model. These navigation paths help guide simple consumers in understanding and navigating relationships. In some cases, however, requests need to span entity sets with no predefined associations. Such requests can be sent to the special resource $crossjoin instead of an individual entity set. The cross join of a list of entity sets is the Cartesian product of the listed entity sets, represented as a collection of complex type instances that have a navigation property with cardinality to-one for each participating entity set, and queries across entity sets can be formulated using these navigation properties. See [OData-URL, section 4.15] for details. Where useful navigations exist it is beneficial to expose those as explicit navigation properties in the model, but the ability to pose queries that span entity sets not related by an association provides a mechanism for advanced consumers to use more flexible join conditions. Example 40: if Sale had a string property ProductID instead of the navigation property Product, a “join” between Sales and Products could be accessed via the $crossjoin resource GET /service/$crossjoin(Products,Sales) ?$expand=Products($select=Name),Sales($select=Amount) &$filter=Products/ID eq Sales/ProductID results in { "@context": "$metadata#Collection(Edm.ComplexType)", "value": [ { "Products": { "Name": "Paper" }, "Sales": { "Amount": 1 } }, { "Products": { "Name": "Sugar" }, "Sales": { "Amount": 2 } }, … ] } Example 41: using the $crossjoin resource for aggregate queries GET /service/$crossjoin(Products,Sales) ?$apply=filter(Products/ID eq Sales/ProductID) /groupby((Products/Name), aggregate(Sales/Amount with sum as Total)) results in { "@context": "$metadata#Collection(Edm.ComplexType)", "value": [ { "Products": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Products": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 8 }, { "Products": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 4 } ] }
The entity container may be annotated in the same way as entity sets to express which aggregate queries are supported, see section 5.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 32 of 69
Standards Track Work Product
5 Vocabulary for Data Aggregation The following terms are defined in the vocabulary for data aggregation [OData-VocAggr].
5.1 Aggregation Capabilities The term ApplySupported can be applied to an entity set, an entity type, or a collection if the target expression of the annotation starts with an entity container (see example 43). It describes the aggregation capabilities of the annotated target. If present, it implies that instances of the annotated target can contain dynamic properties as an effect of $apply even if they do not specify the OpenType attribute, see [OData-CSDL, section 6.3]. The term has a complex type with the following properties: The Transformations collection lists all supported set transformations. Allowed values are the names of the standard transformations introduced in sections 3 and 6, and namespace-qualified names identifying a servicedefined bindable function. If Transformations is omitted the server supports all transformations defined by this specification. The CustomAggregationMethods collection lists supported custom aggregation methods. Allowed values are namespace-qualified names identifying service-specific aggregation methods. If omitted, no custom aggregation methods are supported. 🚧 Rollup is reserved for later versions of this specifications. The functional scope of this version of the specification is expressed by giving Rollup the value None. A non-empty GroupableProperties indicates that only the listed properties of the annotated target can be used in groupby. A non-empty AggregatableProperties indicates that only the listed properties of the annotated target can be used in aggregate, optionally restricted to the specified aggregation methods. All properties of ApplySupported are optional, so it can be used as a tagging annotation to signal unlimited support of aggregation. The term ApplySupportedDefaults can be applied to an entity container. It allows to specify default support for aggregation capabilities Transformations, CustomAggregationMethods and Rollup that propagate to all collection-valued resources in the container. Annotating a specific collection-valued resource with the term ApplySupported overrides the default support with the specified properties using PATCH semantics: Primitive or collection-valued properties specified in ApplySupported replace the corresponding properties specified in ApplySupportedDefaults. Complex-valued properties specified in ApplySupported override the corresponding properties specified in ApplySupportedDefaults using PATCH semantics recursively. Properties specified neither in ApplySupported nor in ApplySupportedDefault have their default value. Example 42: an entity container with default support for everything defined in this specification <EntityContainer Name="SalesData"> <Annotation Term="Aggregation.ApplySupportedDefaults" /> … </EntityContainer> Example 43: Define aggregation support only for the products of a given category <Annotations Target="SalesModel.SalesData/Categories/Products"> <Annotation Term="Aggregation.ApplySupported"> … </Annotation> </Annotations>
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 33 of 69
Standards Track Work Product
5.2 Custom Aggregates The term CustomAggregate allows defining dynamic properties that can be used in aggregate. No assumptions can be made on how the values of these custom aggregates are calculated, whether they are null, and which input values are used. When applied to an entity set, an entity type, or a collection if the target expression of the annotation starts with an entity container, the annotation specifies custom aggregates that are available for its instances and for aggregated instances resulting from these instances. When applied to an entity container, the annotation specifies custom aggregates whose input set may span multiple entity sets within the container. A custom aggregate is identified by the value of the Qualifier attribute when applying the term. The value of the Qualifier attribute is the name of the dynamic property. The name MUST NOT collide with the names of other custom aggregates of the same model element. The value of the annotation is a string with the qualified name of a primitive type or type definition in scope that specifies the type returned by the custom aggregate. If the custom aggregate is associated with an entity set, entity type, or collection, the value of the Qualifier attribute MAY be identical to the name of a declared property of the instances in this set or collection. In these cases, the value of the annotation MUST have the same value as the Type attribute of the declared property. This is typically done when the custom aggregate is used as a default aggregate for that property. In this case the name refers to the custom aggregate within an aggregate expression without a with clause, and to the property in all other cases. If the custom aggregate is associated with an entity container, the value of the Qualifier attribute MUST NOT collide with the names of any entity container children. Example 44: Sales forecasts are modeled as a custom aggregate of the Sale entity type because it belongs there. For the budget, there is no appropriate structured type, so it is modeled as a custom aggregate of the SalesData entity container. <Annotations Target="SalesModel.SalesData/Sales"> <Annotation Term="Aggregation.CustomAggregate" Qualifier="Forecast" String="Edm.Decimal" /> </Annotations> <Annotations Target="SalesModel.SalesData"> <Annotation Term="Aggregation.CustomAggregate" Qualifier="Budget" String="Edm.Decimal" /> </Annotations> These custom aggregates can be used in the aggregate transformation: GET /service/Sales?$apply=groupby((Time/Month),aggregate(Forecast)) and: GET /service/$crossjoin(Time)?$apply=groupby((Time/Year),aggregate(Budget))
5.3 Context-Defining Properties Sometimes the value of a property or custom aggregate is only well-defined within the context given by values of other properties, e.g. a postal code together with its country, or a monetary amount together with its currency unit. These context-defining properties can be listed with the term ContextDefiningProperties whose type is a collection of property paths. If present, the context-defining properties SHOULD be used as grouping properties when aggregating the annotated property or custom aggregate, or alternatively be restricted to a single value by a pre-filter operation. Services MAY respond with 400 Bad Request if the context-defining properties are not sufficiently specified for calculating a meaningful aggregate value.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 34 of 69
Standards Track Work Product
5.4 Annotation Example Example 45: This simplified Sales entity set has a single aggregatable property Amount whose context is defined by the Code property of the related Currency, and a custom aggregate Forecast with the same context. The Code property of Currencies is groupable. All other properties are neither groupable nor aggregatable. <EntityType Name="Currency"> <Key> <PropertyRef Name="Code" /> </Key> <Property Name="Code" Type="Edm.String" /> <Property Name="Name" Type="Edm.String"> <Annotation Term="Core.IsLanguageDependent" /> </Property> </EntityType> <EntityType Name="Sale"> <Key> <PropertyRef Name="ID" /> </Key> <Property Name="ID" Type="Edm.String" Nullable="false" /> <Property Name="Amount" Type="Edm.Decimal" Scale="variable"> <Annotation Term="Aggregation.ContextDefiningProperties"> <Collection> <PropertyPath>Currency/Code</PropertyPath> </Collection> </Annotation> </Property> <NavigationProperty Name="Currency" Type="SalesModel.Currency" Nullable="false" /> </EntityType> <EntityContainer Name="SalesData"> <EntitySet Name="Sales" EntityType="SalesModel.Sale"> <Annotation Term="Aggregation.ApplySupported"> <Record> <PropertyValue Property="AggregatableProperties"> <Collection> <Record> <PropertyValue Property="Property" PropertyPath="Amount" /> </Record> </Collection> </PropertyValue> <PropertyValue Property="GroupableProperties"> <Collection> <PropertyPath>Currency</PropertyPath> </Collection> </PropertyValue> </Record> </Annotation> <Annotation Term="Aggregation.CustomAggregate" Qualifier="Forecast" String="Edm.Decimal"> <Annotation Term="Aggregation.ContextDefiningProperties"> <Collection> <PropertyPath>Currency/Code</PropertyPath> </Collection> </Annotation> </Annotation> </EntitySet> <EntitySet Name="Currencies" EntityType="SalesModel.Currency"> <Annotation Term="Aggregation.ApplySupported"> <Record> <PropertyValue Property="GroupableProperties">
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 35 of 69
Standards Track Work Product
<Collection> <PropertyPath>Code</PropertyPath> </Collection> </PropertyValue> </Record> </Annotation> </EntitySet> </EntityContainer>
5.5 Hierarchies A hierarchy is an arrangement of entities whose values are represented as being “above”, “below”, or “at the same level as” one another.
🚧 Recursive hierarchies are defined in the following subsection. Any list of properties can be viewed as a leveled
hierarchy with a fixed number of levels, for example, year, quarter and month, but this is not made explicit in the OData service.
5.5.1 Recursive Hierarchy A recursive hierarchy is defined on a collection of entities by determining which entities are part of the hierarchy and giving every such entity a single primitive non-null value that uniquely identifies it within the hierarchy. These entities are called nodes, and the primitive value is called the node identifier, and associating with every node zero or more nodes from the same collection, called its parent nodes. The recursive hierarchy is described in the model by an annotation of the entity type with the complex term RecursiveHierarchy with these properties: The NodeProperty MUST be a path with single-valued segments ending in a primitive property. This property holds the node identifier of an entity that is a node in the hierarchy. The ParentNavigationProperty MUST be a collection-valued or nullable single-valued navigation property path that addresses the entity type annotated with this term. It navigates from an entity that is a node in the hierarchy to its parent nodes. The term RecursiveHierarchy can only be applied to entity types, and MUST be applied with a qualifier, which is used to reference the hierarchy in transformations operating on recursive hierarchies and in hierarchy functions. The same entity can serve as nodes in different recursive hierarchies, given different qualifiers. A root node is a node without parent nodes. A recursive hierarchy can have one or more root nodes. A node is a child node of its parent nodes, a node without child nodes is a leaf node. Two nodes with a common parent node are sibling nodes and so are two root nodes. The descendants with maximum distance d ≥ 1 of a node are its child nodes and, if d > 1, the descendants of these child nodes with maximum distance d − 1. The descendants are the descendants with maximum distance d = ∞. A node together with its descendants forms a sub-hierarchy of the hierarchy. The ancestors with maximum distance d ≥ 1 of a node are its parent nodes and, if d > 1, the ancestors of these parent nodes with maximum distance d − 1. The ancestors are the ancestors with maximum distance d = ∞. The ParentNavigationProperty MUST be such that no node is an ancestor of itself, in other words: cycles are forbidden. 5.5.1.1 Hierarchy Functions For testing the position of a given entity in a recursive hierarchy, the Aggregation vocabulary [OData-VocAggr] defines unbound functions. These have
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 36 of 69
Standards Track Work Product
a parameter pair HierarchyNodes, HierarchyQualifier where HierarchyNodes is a collection and HierarchyQualifier is the qualifier of a RecursiveHierarchy annotation on its common entity type. The node identifiers in this collection define the recursive hierarchy. a parameter Node that contains the node identifier of the entity to be tested. Note that the test result depends only on this node identifier, not on any other property of the given entity additional parameters, depending on the type of test (see below) a Boolean return value for the outcome of the test. The following functions are defined: isnode tests if the given entity is a node of the hierarchy. isroot tests if the given entity is a root node of the hierarchy. isdescendant tests if the given entity is a descendant with maximum distance MaxDistance of an ancestor node (whose node identifier is given in a parameter Ancestor), or equals the ancestor if IncludeSelf is true. isancestor tests if the given entity is an ancestor with maximum distance MaxDistance of a descendant node (whose node identifier is given in a parameter Descendant), or equals the descendant if IncludeSelf is true. issibling tests if the given entity and another entity (whose node identifier is given in a parameter Other) are sibling nodes. isleaf tests if the given entity is a leaf node.
5.5.2 Hierarchy Examples The hierarchy terms can be applied to the Example Data Model. ⚠ Example 46: leveled hierarchies for products and time, and a recursive hierarchy for the sales organizations: <?xml version="1.0" encoding="UTF-8" standalone="yes"?> <edmx:Edmx xmlns:edmx="http://docs.oasis-open.org/odata/ns/edmx" Version="4.0"> <edmx:Reference Uri="https://docs.oasis-open.org/odata/odata-dataaggregation-ext/v4.0/cs04/vocabularies/Org.OData.Aggregation.V1.xml"> <edmx:Include Alias="Aggregation" Namespace="Org.OData.Aggregation.V1" /> </edmx:Reference> <edmx:DataServices> <Schema xmlns="http://docs.oasis-open.org/odata/ns/edm" Alias="SalesModel" Namespace="org.example.odata.salesservice"> <Annotations Target="SalesModel.SalesOrganization"> <Annotation Term="Aggregation.RecursiveHierarchy" Qualifier="SalesOrgHierarchy"> <Record> <PropertyValue Property="NodeProperty" PropertyPath="ID" /> <PropertyValue Property="ParentNavigationProperty" PropertyPath="Superordinate" /> </Record> </Annotation> </Annotations> </Schema> </edmx:DataServices> </edmx:Edmx>
The recursive hierarchy SalesOrgHierarchy can be used in functions with the $filter system query option. Example 47: requesting all organizations below EMEA GET /service/SalesOrganizations?$filter=Aggregation.isdescendant( HierarchyNodes=$root/SalesOrganizations, HierarchyQualifier='SalesOrgHierarchy',
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 37 of 69
Standards Track Work Product
Node=ID, Ancestor='EMEA') results in { "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "EMEA Central", "Name": "EMEA Central" }, { "ID": "Sales Netherlands", "Name": "Sales Netherlands" }, { "ID": "Sales Germany", "Name": "Sales Germany" }, { "ID": "EMEA South", "Name": "EMEA South" }, … { "ID": "EMEA North", "Name": "EMEA North" }, … ] } Example 48: requesting just those organizations directly below EMEA GET /service/SalesOrganizations?$filter=Aggregation.isdescendant( HierarchyNodes=$root/SalesOrganizations, HierarchyQualifier='SalesOrgHierarchy', Node=ID, Ancestor='EMEA', MaxDistance=1) results in { "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "EMEA Central", "Name": "EMEA Central" }, { "ID": "EMEA South", "Name": "EMEA South" }, { "ID": "EMEA North", "Name": "EMEA North" }, … ] } Example 49: just the lowest-level organizations GET /service/SalesOrganizations?$filter=Aggregation.isleaf( HierarchyNodes=$root/SalesOrganizations, HierarchyQualifier='SalesOrgHierarchy', Node=ID) results in { "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "Sales Office London", "Name": "Sales Office London" }, { "ID": "Sales Office New York", "Name": "Sales Office New York" }, … ] } Example 50: the lowest-level organizations including their superordinate’s ID GET /service/SalesOrganizations?$filter=Aggregation.isleaf( HierarchyNodes=$root/SalesOrganizations, HierarchyQualifier='SalesOrgHierarchy', Node=ID) &$expand=Superordinate($select=ID)
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 38 of 69
Standards Track Work Product
results in { "@context": "$metadata#SalesOrganizations(*,Superordinate(ID))", "value": [ { "ID": "Sales Office London", "Name": "Sales Office London", "Superordinate": { "ID": "EMEA United Kingdom" } }, { "ID": "Sales Office New York", "Name": "Sales Office New York", "Superordinate": { "ID": "US East" } }, … ] } Example 51: the sales IDs involving sales organizations from EMEA
GET /service/Sales?$select=ID&$filter=Aggregation.isdescendant( HierarchyNodes=$root/SalesOrganizations, HierarchyQualifier='SalesOrgHierarchy', Node=SalesOrganization/ID, Ancestor='EMEA') results in { "@context": "$metadata#Sales(ID)", "value": [ { "ID": 6 }, { "ID": 7 }, { "ID": 8 } ] }
Further examples for recursive hierarchies using transformations operating on the hierarchy structure are provided in section 7.9.
5.6 Functions on Aggregated Entities Service-defined bound functions that serve as set transformations MAY be annotated with the term AvailableOnAggregates to indicate that they are applicable to aggregated entities under specific conditions: The RequiredProperties collection lists all properties that must be available in the aggregated entities; otherwise, the annotated function will be inapplicable. Example 52: assume the product is an implicit input for a function bound to a collection of Sales, then aggregating away the product makes this function inapplicable.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 39 of 69
Standards Track Work Product
6 Hierarchical Transformations The transformations defined in this section are called hierarchical, because they make use of a recursive hierarchy and are defined in terms of hierarchy functions introduced in the previous section. The transformations ancestors and descendants do not define an order on the output set. An order can be imposed by a subsequent orderby or traverse transformation or a $orderby. The output set of traverse is in preorder or postorder. The algorithmic descriptions of the transformations make use of a union of collections, this is defined as an unordered collection containing the items from all these collections and from which duplicates have been removed. The notation u[t] is used to denote the value of a property t, possibly preceded by a type-cast segment, in an instance u. It is also used to denote the value of a single-valued data aggregation path t, evaluated relative to u. The value of a collection-valued data aggregation path is denoted in the Γ notation by γ(u, t). The notations introduced here are used throughout the following subsections.
6.1 Common Parameters for Hierarchical Transformations The parameter lists defined in the following subsections have three mandatory parameters in common. The recursive hierarchy is defined by a parameter pair (H, Q), where H and Q MUST be specified as the first and second parameter. Here, H MUST be an expression of type Collection(Edm.EntityType) starting with $root that has no multiple occurrences of the same entity. H identifies the collection of node entities forming a recursive hierarchy based on an annotation of their common entity type with term RecursiveHierarchy with a Qualifier attribute whose value MUST be provided in Q. The property paths referenced by NodeProperty and ParentNavigationProperty in the RecursiveHierarchy annotation must be evaluable for the nodes in the recursive hierarchy, otherwise the service MUST reject the request. The NodeProperty is denoted by q in this section. The third parameter MUST be a data aggregation path p with single- or collection-valued segments whose last segment MUST be a primitive property. The node identifier(s) of an instance u in the input set are the primitive values in γ(u, p), they are reached via p starting from u. Let p = p1/ … /pk/r with k ≥ 0 be the concatenation where each sub-path p1, … , pk consists of a collection-valued segment that is preceded by zero or more single-valued segments, and either r consists of one or more single-valued segments or k ≥ 1 and /r is absent. Each segment can be prefixed with a type cast.
6.2 Hierarchical Transformations Producing a Subset These transformations produce an output set that consists of certain instances from their input set, possibly with repetitions or in a different order.
6.2.1 Transformations ancestors and descendants In the simple case, the ancestors transformation takes an input set consisting of instances that belong to a recursive hierarchy (H, Q). It determines a subset A of the input set and then determines the set of ancestors of A that were already contained in the input set. Its output set is the ancestors set, optionally including A. In the more complex case, the instances in the input set are instead related to nodes in a recursive hierarchy. Then the ancestors transformation determines a subset A of the input set consisting of instances that are related to certain nodes in the hierarchy, called start nodes. The ancestors of these start nodes are then determined, and the output set consists of instances of the input set that are related to the ancestors, or optionally to the start nodes. The descendants transformation works analogously, but with descendants. H , Q and p are the first three parameters defined above.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 40 of 69
Standards Track Work Product
The fourth parameter is a transformation sequence T composed of transformations listed section 3.3 or section 6.2.1 and of service-defined bound functions whose output set is a subset of their input set. A is the output set of this sequence applied to the input set. The fifth parameter d is optional and takes an integer greater than or equal to 1 that specifies the maximum distance between start nodes and ancestors or descendants to be considered. An optional final keep start parameter drives the optional inclusion of the subset or start nodes. The output set of the transformation ancestors(H, Q, p, T , d, keep start) or descendants(H, Q, p, T , d, keep start) is defined as the union of the output sets of transformations F (u) applied to the input set for all u in A. For a given instance u, the transformation F (u) determines all instances of the input set whose node identifier is an ancestor or descendant of the node identifier of u: If p contains only single-valued segments, then, for ancestors, F (u) = filter(Aggregation.isancestor( HierarchyNodes = H, HierarchyQualifier = ′Q′, Node = p, Descendant = u[p], MaxDistance = d, IncludeSelf = true)) or, for descendants, F (u) = filter(Aggregation.isdescendant( HierarchyNodes = H, HierarchyQualifier = ′Q′, Node = p, Ancestor = u[p], MaxDistance = d, IncludeSelf = true)). Otherwise p = p1/ … /pk/r with k ≥ 1, in this case the output set of the transformation F (u) is defined as the union of the output sets of transformations G(n) applied to the input set for all n in γ(u, p). The output set of G(n) consists of the instances of the input set whose node identifier is an ancestor or descendant of the node identifier n: For ancestors, G(n) = filter( p1/any(y1 : y1/p2/any(y2 : ⋱ yk−1/pk/any(yk : Aggregation.isancestor( HierarchyNodes = H, HierarchyQualifier = ′Q′, Node = yk/r, Descendant = n, MaxDistance = d, IncludeSelf = true ) ) ⋰
) ) )
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 41 of 69
Standards Track Work Product
or, for descendants, G(n) = filter( p1/any(y1 : y1/p2/any(y2 : ⋱ yk−1/pk/any(yk : Aggregation.isdescendant( HierarchyNodes = H, HierarchyQualifier = ′Q′, Node = yk/r, Ancestor = n, MaxDistance = d, IncludeSelf = true ) ) ⋰
) ) ) where y1, … , yk denote lambdaVariableExprs as defined in [OData-ABNF] and /r may be absent. If parameter d is absent, the parameter MaxDistance = d is omitted. If keep start is absent, the parameter IncludeSelf = true is omitted. Since the output set of ancestors is constructed as a union, no instance from the input set will occur more than once in it, even if, for example, a sale is related to both a sales organization and one of its ancestor organizations. For descendants, analogously. Example 53: Request based on the SalesOrgHierarchy defined in Hierarchy Examples, with Superordinate/$ref expanded to illustrate the hierarchy relation GET /service/SalesOrganizations?$apply= ancestors($root/SalesOrganizations,SalesOrgHierarchy,ID, filter(contains(Name,'East') or contains(Name,'Central'))) &$expand=Superordinate/$ref results in { "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "EMEA", "Name": "EMEA", "Superordinate": { "@id": "SalesOrganizations('Sales')" } }, { "ID": "US", "Name": "US", "Superordinate": { "@id": "SalesOrganizations('Sales')" } }, { "ID": "Sales", "Name": "Sales", "Superordinate": null } ] } Example 54: Request based on the SalesOrgHierarchy defined in Hierarchy Examples, with Superordinate/$ref expanded to illustrate the hierarchy relation GET /service/SalesOrganizations?$apply= descendants($root/SalesOrganizations,SalesOrgHierarchy,ID, filter(Name eq 'US'),keep start) &$expand=Superordinate/$ref results in
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 42 of 69
Standards Track Work Product
{ "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "US West", "Name": "US West", "Superordinate": { "@id": "SalesOrganizations('US')" } }, { "ID": "US", "Name": "US", "Superordinate": { "@id": "SalesOrganizations('Sales')" } }, { "ID": "US East", "Name": "US East", "Superordinate": { "@id": "SalesOrganizations('US')" } } ] }
⚠ Example 55: Input set and recursive hierarchy from two different entity sets GET /service/Sales?$apply= ancestors($root/SalesOrganizations, SalesOrgHierarchy, SalesOrganization/ID, filter(contains(SalesOrganization/Name,'East') or contains(SalesOrganization/Name,'Central')), keep start) results in { "@context": "$metadata#Sales", "value": [ { "ID": "4", "Amount": 8, "SalesOrganization": { "ID": "US East", "Name": "US East" } }, { "ID": "5", "Amount": 4, "SalesOrganization": { "ID": "US East", "Name": "US East" } }, { "ID": "6", "Amount": 2, "SalesOrganization": { "ID": "EMEA Central", "Name": "EMEA Central" } }, { "ID": "7", "Amount": 1, "SalesOrganization": { "ID": "EMEA Central", "Name": "EMEA Central" } }, { "ID": "8", "Amount": 2, "SalesOrganization": { "ID": "EMEA Central", "Name": "EMEA Central" } } ] }
6.2.2 Transformation traverse The traverse transformation returns instances of the input set that are or are related to nodes of a given recursive hierarchy in a specified tree order.
🚧 This version of the specification defines the behavior of the traverse transformation only in recursive hierarchies where RecursiveHierarchy/ParentNavigationProperty is single-valued. H , Q and p are the first three parameters defined above. The fourth parameter h of the traverse transformation is either preorder or postorder. Let H ′ be the collection of root nodes in the recursive hierarchy (H, Q). Nodes in H ′ are called start nodes in this subsection (see example 91). Let o be the list of all following parameters that are expressions which could also be passed as a $orderby system query option, if there are any. If o is present, the transformation stable-sorts H ′ by o.
🚧 Future versions of this specification MAY allow an optional fifth parameter that comes before the parameter list o and could not be passed as a $orderby system query option.
The instances in the input set are related to one node (if p is single-valued) or multiple nodes (if p is collection-valued) in the recursive hierarchy. Given a node x, denote by F^(x) the collection of all instances in the input set that are related to
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 43 of 69
Standards Track Work Product
x; these collections can overlap. For each u in F^(x), the output set contains one instance that comprises the properties of u and additional properties that identify the node x. These additional properties are independent of u and are bundled into an instance called σ(x). For example, if a sale u is related to two sales organizations and hence contained in both F^(x1) and F^(x2), the output set will contain two instances (u, σ(x1)) and (u, σ(x2)) and σ(xi) contributes a navigation property SalesOrganization. A transformation F (x) is defined below such that F^(x) is the output set of F (x) applied to the input set of the traverse transformation. Given a node x, the formulas below contain the transformation ΠG(σ(x)) in order to inject the properties of σ(x) into the instances in F^(x); this uses the function ΠG that is defined in the simple grouping section. Further, G is a list of data aggregation paths that shall be present in the output set, and σ is a function that maps each hierarchy node x to an instance of the input type containing the paths from G. As a consequence of the following definitions, only single-valued properties and “final segments from G” are nested into σ(x), therefore the behavior of ΠG(σ(x)) is well-defined. The definition of σ(x) makes use of a function a(ε, t, x), which returns a sparsely populated instance u in which only the path t has a value, namely u[t] = x. Three cases are distinguished: 1. Case where the recursive hierarchy is defined on the input set This case applies if the paths p and q are equal. Let σ(x) = x and let G be a list containing all structural and navigation properties of the entity type of H . In this case ΠG(σ(x)) injects all properties of x into the instances of the output set. (See example 57.) 2. Case where the recursive hierarchy is defined on the related entity type addressed by a navigation property path This case applies if p′ is a non-empty navigation property path and p′′ an optional type-cast segment such that p equals the concatenated path p′/p′′/q. Let σ(x) = a(ε, p′/p′′, x) and let G = (p′). In this case ΠG(σ(x)) injects the whole related entity x into the instances of the output set. The navigation property path p′ is expanded by default. (See example 58.) 3. Case where the recursive hierarchy is related to the input set only through equality of node identifiers, not through navigation If neither case 1 nor case 2 applies, let σ(x) = a(ε, p, x[q]) and let G = (p). In this case ΠG(σ(x)) injects only the node identifier of x into the instances of the output set. Here paths are considered equal if their non-type-cast segments refer to the same model elements when evaluated relative to the input set (see example 59). The function a(u, t, x) takes an instance, a path and another instance as arguments and is defined recursively as follows: 1. If u equals the special symbol ε, set u to a new instance of the input type without properties and without entity-id. 2. If t contains only one segment other than a type cast, let t1 = t, and let x′ = x, then go to step 6. 3. Otherwise, let t1 be the first property segment in t, possibly together with a preceding type-cast segment, let t2 be any type-cast segment that immediately follows, and let t3 be the remainder such that t equals the concatenated path t1/t2/t3 where /t2 may be absent. 4. Let u′ be an instance of the type of t1/t2 without properties and without entity-id. 5. Let x′ = a(u′, t3, x). 6. If t1 is single-valued, let u[t1] = x′. 7. If t1 is collection-valued, let u[t1] be a collection consisting of one item x′. 8. Return u. (See example 88.) Since start nodes are root nodes, σ(x) is computed exactly once for every node x, as part of the recursive formula for R(x) given below.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 44 of 69
Standards Track Work Product
Let r1, … , rn be a sequence of the start nodes in H ′ preserving the order of H ′ stable-sorted by o. Then the transformation traverse(H, Q, p, h, o) is defined as equivalent to concat(R(r1), … , R(rn)). R(x) is a transformation producing the specified tree order for a sub-hierarchy of H with root node x. Let c1, … , cm with m ≥ 0 be an order-preserving sequence of the children of x in (H, Q). The recursive formula for R(x) is as follows: If h = preorder, then R(x) = concat(F (x)/ΠG(σ(x)), R(c1), … , R(cm)). If h = postorder, then R(x) = concat(R(c1), … , R(cm), F (x)/ΠG(σ(x))). The absence of cycles guarantees that the recursion terminates. F (x) is a transformation that determines for the specified node x the instances of the input set having the same node identifier as x. If p contains only single-valued segments, then F (x) = filter(p eq x[q]). Otherwise p = p1/ … /pk/r with k ≥ 1 and F (x) = filter( p1/any(y1 : y1/p2/any(y2 : ⋱ yk−1/pk/any(yk : yk/r eq x[q] ) ⋰
) ) ) where y1, … , yk denote lambdaVariableExprs and /r may be absent. Example 56: Based on the SalesOrgHierarchy defined in Hierarchy Examples GET /service/SalesOrganizations?$apply= descendants($root/SalesOrganizations,SalesOrgHierarchy,ID, Name eq 'US',keep start) /ancestors($root/SalesOrganizations,SalesOrgHierarchy,ID, contains(Name,'East'),keep start) /traverse($root/SalesOrganizations,SalesOrgHierarchy,ID,preorder) &$expand=Superordinate/$ref results in { "@context": "$metadata#SalesOrganizations", "value": [ { "ID": "US", "Name": "US", "Superordinate": { "@id": "SalesOrganizations('Sales')" } }, { "ID": "US East", "Name": "US East", "Superordinate": { "@id": "SalesOrganizations('US')" } } odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 45 of 69
Standards Track Work Product
] } Example 57: Postorder traversal of organizations in the hierarchy defined in Hierarchy Examples with p = q = ID (case 1 of the definition of σ(x) ). In this case ΠG(σ(x)) writes back the entire node into the output set of T . GET /service/SalesOrganizations?$apply= traverse($root/SalesOrganizations,SalesOrgHierarchy,ID,postorder) &$select=ID,Name &$expand=Superordinate($select=ID) results in { "@context": "$metadata#SalesOrganizations(ID,Name,Superordinate(ID))", "value": [ { "ID": "US West", "Name": "US West", "Superordinate": { "ID": "US" } }, { "ID": "US East", "Name": "US East", "Superordinate": { "ID": "US" } }, { "ID": "US", "Name": "US", "Superordinate": { "ID": "Sales" } }, { "ID": "EMEA Central", "Name": "EMEA Central", "Superordinate": { "ID": "EMEA" } }, { "ID": "EMEA", "Name": "EMEA", "Superordinate": { "ID": "Sales" } }, { "ID": "Sales", "Name": "Sales", "Superordinate": null } ] }
⚠ Example 58: Postorder traversal of sales per organization in the hierarchy defined in Hierarchy Examples with p = p′/q = SalesOrganization/ID and p′ = SalesOrganization (case 2 of the definition of σ(x)). GET /service/Sales?$apply=traverse( $root/SalesOrganizations, SalesOrgHierarchy, SalesOrganization/ID, postorder) &$select=ID &$expand=SalesOrganization($select=ID) The result contains each sale once for every organization to which it belongs, directly or indirectly. { "@context": "$metadata#Sales(ID,SalesOrganization(ID))", "value": [ { "ID": 1, "SalesOrganization": { "ID": "US West" } }, { "ID": 2, "SalesOrganization": { "ID": "US West" } }, { "ID": 3, "SalesOrganization": { "ID": "US West" } }, { "ID": 4, "SalesOrganization": { "ID": "US East" } }, { "ID": 5, "SalesOrganization": { "ID": "US East" } }, { "ID": 1, "SalesOrganization": { "ID": "US" } }, { "ID": 2, "SalesOrganization": { "ID": "US" } }, { "ID": 3, "SalesOrganization": { "ID": "US" } }, { "ID": 4, "SalesOrganization": { "ID": "US" } }, { "ID": 5, "SalesOrganization": { "ID": "US" } }, … ] }
⚠ Example 59: Although p = ID and q = ID, they are not equal in the sense of case 1, because they are evaluated relative to different entity sets. Hence, this is an example of case 3 of the definition of σ(x), where no Sales/ID matches a SalesOrganizations/ID, that is, all F (x) have empty output sets. odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 46 of 69
Standards Track Work Product
GET /service/Sales?$apply=traverse( $root/SalesOrganizations, SalesOrgHierarchy, ID, postorder) results in { "@context": "$metadata#Sales(ID,SalesOrganization(ID))", "value": [] }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 47 of 69
Standards Track Work Product
7 Examples The following examples show some common aggregation-related questions that can be answered by combining the transformations defined in sections 3 and 6.
7.1 Requesting Distinct Values Grouping without specifying a set transformation returns the distinct combination of the grouping properties. Example 60: GET /service/Customers?$apply=groupby((Name)) results in { "@context": "$metadata#Customers(Name)", "value": [ { "Name": "Luc" }, { "Name": "Joe" }, { "Name": "Sue" } ] } Note that “Sue” appears only once although the customer base contains two different Sues.
Aggregation is also possible across related entities. Example 61: customers that bought something GET /service/Sales?$apply=groupby((Customer/Name)) results in { "@context": "$metadata#Sales(Customer(Name))", "value": [ { "Customer": { "Name": "Joe" } }, { "Customer": { "Name": "Sue" } } ] } Since groupby expands navigation properties in grouping properties by default, this is the same result as if the request would include a $expand=Customer($select=Name). The groupby removes all other properties. Note that “Luc” does not appear in the aggregated result as he hasn’t bought anything and therefore there are no sales entities that refer/navigate to Luc. However, even though both Sues bought products, only one “Sue” appears in the aggregate result. Including properties that guarantee the right level of uniqueness in the grouping can repair that. Example 62: GET /service/Sales?$apply=groupby((Customer/Name,Customer/ID)) results in { "@context": "$metadata#Sales(Customer(Name,ID))", "value": [ { "Customer": { "Name": "Joe", "ID": "C1" } }, { "Customer": { "Name": "Sue", "ID": "C2" } }, { "Customer": { "Name": "Sue", "ID": "C3" } } odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 48 of 69
Standards Track Work Product
] } This could also have been formulated as GET /service/Sales?$apply=groupby((Customer)) &$expand=Customer($select=Name,ID) Example 63: Grouping by navigation property Customer
GET /service/Sales?$apply=groupby((Customer)) results in { "@context": "$metadata#Sales(Customer())", "value": [ { "Customer": { "ID": "C1", "Name": "Joe", "Country": "USA" } }, { "Customer": { "ID": "C2", "Name": "Sue", "Country": "USA" } }, { "Customer": { "ID": "C3", "Name": "Sue", "Country": "Netherlands" } } ] } Example 64: the first question in the motivating example in section 2.3, which customers bought which products, can now be expressed as GET /service/Sales?$apply=groupby((Customer/Name,Customer/ID,Product/Name)) and results in { "@context": "$metadata#Sales(Customer(Name,ID),Product(Name))", "value": [ { "Customer": { "Name": "Joe", "ID": "C1" }, "Product": { "Name": "Coffee"} }, { "Customer": { "Name": "Joe", "ID": "C1" }, "Product": { "Name": "Paper" } }, { "Customer": { "Name": "Joe", "ID": "C1" }, "Product": { "Name": "Sugar" } }, { "Customer": { "Name": "Sue", "ID": "C2" }, "Product": { "Name": "Coffee"} }, { "Customer": { "Name": "Sue", "ID": "C2" }, "Product": { "Name": "Paper" } }, { "Customer": { "Name": "Sue", "ID": "C3" }, "Product": { "Name": "Paper" } }, { "Customer": { "Name": "Sue", "ID": "C3" }, "Product": { "Name": "Sugar" } } ] }
⚠ Example 65: grouping by properties of subtypes GET /service/Products?$apply=groupby((SalesModel.FoodProduct/Rating, SalesModel.NonFoodProduct/RatingClass)) results in { "@context": "$metadata#Products(SalesModel.FoodProduct/Rating, SalesModel.NonFoodProduct/RatingClass)", "value": [ { "@type": "#SalesModel.FoodProduct", "Rating": 5 }, { "@type": "#SalesModel.FoodProduct", "Rating": null }, { "@type": "#SalesModel.NonFoodProduct", "RatingClass": "average" }, odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 49 of 69
Standards Track Work Product
{ "@type": "#SalesModel.NonFoodProduct", "RatingClass": null } ] }
⚠ Example 66: grouping by a property of a subtype GET /service/Products?$apply=groupby((SalesModel.FoodProduct/Rating)) results in a third group representing entities with no SalesModel.FoodProduct/Rating, including the SalesModel.NonFoodProducts: { "@context": "$metadata#Products(@Core.AnyStructure)", "value": [ { "@type": "#SalesModel.FoodProduct", "Rating": 5 }, { "@type": "#SalesModel.FoodProduct", "Rating": null }, { } ] }
7.2 Standard Aggregation Methods The client may specify one of the predefined aggregation methods min, max, sum, average, and countdistinct, or a custom aggregation method, to aggregate an aggregatable expression. Expressions defining an aggregate method specify an alias. The aggregated values are returned in a dynamic property whose name is determined by the alias. Example 67: GET /service/Products?$apply=groupby((Name), aggregate(Sales/Amount with sum as Total)) results in { "@context": "$metadata#Products(Name,Total)", "value": [ { "Name": "Coffee", "Total@type": "Decimal", "Total": 12 }, { "Name": "Paper", "Total@type": "Decimal", "Total": 8 }, { "Name": "Pencil", "Total": null }, { "Name": "Sugar", "Total@type": "Decimal", "Total": 4 } ] } Note that the base set of the request is Products, so there is a result item for product Pencil even though there are no sales items. The input set for the aggregation in the third row is I consisting of the pencil, p = q/r = Sales/Amount, E = Γ(I, q) is empty and A = Γ(E, r) is also empty. The sum over the empty collection is null. Example 68: Compute the aggregate as a property using the aggregate function in $compute: GET /service/Products?$compute=Sales/aggregate(Amount with sum) as Total results in { "@context": "$metadata#Products(*,Total)", "value": [ { "ID": "P2", "Name": "Coffee", "Color": "Brown", "TaxRate": 0.06, "Total@type": "Decimal", "Total": 12 }, { "ID": "P3", "Name": "Paper", "Color": "White", "TaxRate": 0.14, "Total@type": "Decimal", "Total": 8 }, { "ID": "P4", "Name": "Pencil", "Color": "Black", "TaxRate": 0.14, "Total": null }, { "ID": "P1", "Name": "Sugar", "Color": "White", "TaxRate": 0.06, "Total@type": "Decimal", "Total": 4 }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 50 of 69
Standards Track Work Product
] } Example 69: Alternatively, join could be applied to yield a flat structure: GET /service/Products?$apply= join(Sales as TotalSales,aggregate(Amount with sum as Total)) /groupby((Name,TotalSales/Total)) results in { "@context": "$metadata#Products(Name,TotalSales())", "value": [ { "Name": "Coffee", "TotalSales@context": "#Sales(Total)/$entity", "TotalSales": { "Total@type": "Decimal", "Total": 12 } }, { "Name": "Paper", "TotalSales@context": "#Sales(Total)/$entity", "TotalSales": { "Total@type": "Decimal", "Total": 8 } }, { "Name": "Sugar", "TotalSales@context": "#Sales(Total)/$entity", "TotalSales": { "Total@type": "Decimal", "Total": 4 } } ] } Applying outerjoin instead would return an additional entity for product with ID “Pencil” and TotalSales having a null value. Example 70: GET /service/Sales?$apply=groupby((Customer/Country), aggregate(Amount with average as AverageAmount)) results in { "@context": "$metadata#Sales(Customer(Country),AverageAmount)", "value": [ { "Customer": { "Country": "Netherlands" }, "AverageAmount": 1.6666666666666667 }, { "Customer": { "Country": "USA" }, "AverageAmount": 3.8 } ] } Here the AverageAmount is of type Edm.Double. Example 71: $count after navigation property GET /service/Products?$apply=groupby((Name), aggregate(Sales/$count as SalesCount)) results in { "@context": "$metadata#Products(Name,SalesCount)", "value": [ { "Name": "Coffee", "SalesCount@type": "Decimal", "SalesCount": 2 }, { "Name": "Paper", "SalesCount@type": "Decimal", "SalesCount": 4 }, { "Name": "Pencil", "SalesCount@type": "Decimal", "SalesCount": 0 }, { "Name": "Sugar", "SalesCount@type": "Decimal", "SalesCount": 2 } ] }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 51 of 69
Standards Track Work Product
The aggregate function can not only be used in $compute but also in $filter and $orderby: Example 72: Products with an aggregated sales volume of ten or more GET /service/Products?$filter=Sales/aggregate(Amount with sum) ge 10 results in { "@context": "$metadata#Products", "value": [ { "ID": "P2", "Name": "Coffee", "Color": "Brown", "TaxRate": 0.06 }, { "ID": "P3", "Name": "Paper", "Color": "White", "TaxRate": 0.14 } ] } Example 73: Customers in descending order of their aggregated sales volume GET /service/Customers?$orderby=Sales/aggregate(Amount with sum) desc results in { "@context": "$metadata#Customers", "value": [ { "ID": "C2", "Name": "Sue", "Country": "USA" }, { "ID": "C1", "Name": "Joe", "Country": "USA" }, { "ID": "C3", "Name": "Sue", "Country": "Netherlands" }, { "ID": "C4", "Name": "Luc", "Country": "France" } ] } Example 74: Contribution of each sales to grand total sales amount GET /service/Sales?$compute=Amount divby $these/aggregate(Amount with sum) as Contribution results in { "@context": "$metadata#Sales(*,Contribution)", "value": [ { "ID": 1, "Amount": 1, "Contribution@type": "Decimal", "Contribution": 0.0416666666666667 }, { "ID": 2, "Amount": 2, "Contribution@type": "Decimal", "Contribution": 0.0833333333333333 }, { "ID": 3, "Amount": 4, "Contribution@type": "Decimal", "Contribution": 0.1666666666666667 }, { "ID": 4, "Amount": 8, "Contribution@type": "Decimal", "Contribution": 0.3333333333333333 }, { "ID": 5, "Amount": 4, "Contribution@type": "Decimal", "Contribution": 0.1666666666666667 }, { "ID": 6, "Amount": 2, "Contribution@type": "Decimal", "Contribution": 0.0833333333333333 }, { "ID": 7, "Amount": 1, "Contribution@type": "Decimal", "Contribution": 0.0416666666666667 }, { "ID": 8, "Amount": 2, "Contribution@type": "Decimal", "Contribution": 0.0833333333333333 } ] } Example 75: Product categories with at least one product having an aggregated sales amount greater than 10
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 52 of 69
Standards Track Work Product
GET /service/Categories?$filter=Products/any( p:p/Sales/aggregate(Amount with sum) gt 10) results in { "@context": "$metadata#Categories", "value": [ { "ID": "PG1", "Name": "Food" } ] }
The aggregate function can also be applied inside $apply: Example 76: Sales volume per customer in relation to total volume GET /service/Sales?$apply= groupby((Customer),aggregate(Amount with sum as CustomerAmount)) /compute(CustomerAmount divby $these/aggregate(CustomerAmount with sum) as Contribution) &$expand=Customer/$ref results in { "@context": "$metadata#Sales(Customer(),CustomerAmount,Contribution)", "value": [ { "Customer": { "@id": "Customers('C1')" }, "Contribution@type": "Decimal", "Contribution": 0.2916667 }, { "Customer": { "@id": "Customers('C2')" }, "Contribution@type": "Decimal", "Contribution": 0.5 }, { "Customer": { "@id": "Customers('C3')" }, "Contribution@type": "Decimal", "Contribution": 0.2083333 } ] }
7.3 Requesting Expanded Results Example 77: use outerjoin to split up collection-valued navigation properties for grouping GET /service/Customers?$apply=outerjoin(Sales as ProductSales) /groupby((Country,ProductSales/Product/Name)) returns the different combinations of products sold per country: { "@context": "$metadata#Customers(Country,ProductSales())", "value": [ { "Country": "Netherlands", "ProductSales@context": "#Sales(Product(Name))/$entity", "ProductSales": { "Product": { "Name": "Paper" } } }, { "Country": "Netherlands", "ProductSales@context": "#Sales(Product(Name))/$entity", "ProductSales": { "Product": { "Name": "Sugar" } } }, { "Country": "USA", "ProductSales@context": "#Sales(Product(Name))/$entity", "ProductSales": { "Product": { "Name": "Coffee" } } }, { "Country": "USA", "ProductSales@context": "#Sales(Product(Name))/$entity", "ProductSales": { "Product": { "Name": "Paper" } } }, { "Country": "USA", "ProductSales@context": "#Sales(Product(Name))/$entity", "ProductSales": { "Product": { "Name": "Sugar" } } }, { "Country": "France", "ProductSales": null } odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 53 of 69
Standards Track Work Product
] }
7.4 Requesting Custom Aggregates Custom aggregates are defined through the CustomAggregate annotation. They can be associated with an entity set, a collection or an entity container. A custom aggregate can be used by specifying the name of the custom aggregate in the aggregate clause. Example 78: GET /service/Sales?$apply=groupby((Customer/Country), aggregate(Amount with sum as Actual,Forecast)) results in { "@context": "$metadata#Sales(Customer(Country),Actual,Forecast)", "value": [ { "Customer": { "Country": "Netherlands" }, "Actual@type": "Decimal", "Actual": 5, "Forecast@type": "Decimal", "Forecast": 4 }, { "Customer": { "Country": "USA" }, "Actual@type": "Decimal", "Actual": 19, "Forecast@type": "Decimal", "Forecast": 21 } ] }
When associated with an entity set a custom aggregate MAY have the same name as a property of the underlying entity type with the same type as the type returned by the custom aggregate. This is typically done when the aggregate is used as a default aggregate for that property. Example 79: A custom aggregate can be defined with the same name as a property of the same type in order to define a default aggregate for that property. GET /service/Sales?$apply=groupby((Customer/Country),aggregate(Amount)) results in { "@context": "$metadata#Sales(Customer(Country),Amount)", "value": [ { "Customer": { "Country": "Netherlands" }, "Amount": 5 }, { "Customer": { "Country": "USA" }, "Amount": 19 } ] }
7.5 Aliasing A property can be aggregated in multiple ways, each with a different alias. Example 80: GET /service/Sales?$apply=groupby((Customer/Country), aggregate(Amount with sum as Total, Amount with average as AvgAmt)) results in { "@context": "$metadata#Sales(Customer(Country),Total,AvgAmt)",
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 54 of 69
Standards Track Work Product
"value": [ { "Customer": { "Country": "Netherlands" }, "Total@type": "Decimal", "Total": 5, "AvgAmt@type": "Decimal", "AvgAmt": 1.6666667 }, { "Customer": { "Country": "USA" }, "Total@type": "Decimal", "Total": 19, "AvgAmt@type": "Decimal", "AvgAmt": 3.8 } ] }
There is no hard distinction between groupable and aggregatable properties: the same property can be aggregated and used to group the aggregated results. Example 81: GET /service/Sales?$apply=groupby((Amount),aggregate(Amount with sum as Total)) will return all distinct amounts appearing in sales orders and how much money was made with deals of this amount { "@context": "$metadata#Sales(Amount,Total)", "value": [ { "Amount": 1, "Total@type": "Decimal", "Total": 2 }, { "Amount": 2, "Total@type": "Decimal", "Total": 6 }, { "Amount": 4, "Total@type": "Decimal", "Total": 8 }, { "Amount": 8, "Total@type": "Decimal", "Total": 8 } ] }
7.6 Combining Transformations per Group Dynamic property names may be reused in different transformation sequences passed to concat. Example 82: to get the best-selling product per country with sub-totals for every country, the partial results of a transformation sequence and a groupby transformation are concatenated: GET /service/Sales?$apply=concat( groupby((Customer/Country,Product/Name), aggregate(Amount with sum as Total)) /groupby((Customer/Country),topcount(1,Total)), groupby((Customer/Country), aggregate(Amount with sum as Total))) results in { "@context": "$metadata#Sales(Customer(Country),Total)", "value": [ { "Customer": { "Country": "USA" }, "Product": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 3 }, { "Customer": { "Country": "USA" }, "Total@type": "Decimal", "Total": 19 }, { "Customer": { "Country": "Netherlands" }, "Total@type": "Decimal", "Total": 5 } ] }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 55 of 69
Standards Track Work Product
Example 83: transformation sequences are also useful inside groupby: Aggregate the amount by only considering the top two sales amounts per product and country: GET /service/Sales?$apply=groupby((Customer/Country,Product/Name), topcount(2,Amount)/aggregate(Amount with sum as Total)) results in { "@context": "$metadata#Sales(Customer(Country),Product(Name),Total)", "value": [ { "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 3 }, { "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 2 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 2 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 5 } ] } Example 84: concatenation of two different groupings “biggest sale per customer” and “biggest sale per product”, made distinguishable by a dynamic property: GET /service/Sales?$apply=concat( groupby((Customer),topcount(1,Amount))/compute('Customer' as per), groupby((Product),topcount(1,Amount))/compute('Product' as per)) &$expand=Customer($select=ID),Product($select=ID) In the result, Sales entities 4 and 6 occur twice each with contradictory values of the dynamic property per. If a UI consuming the response presents the two groupings in separate columns based on the per property, no contradiction effectively arises. { "@context": "$metadata#Sales(*,per,Customer(ID),Product(ID))", "value": [ { "Customer": { "ID": "C1" }, "Product": { "ID": "P2" }, "ID": "3", "Amount": 4, "per": "Customer" }, { "Customer": { "ID": "C2" }, "Product": { "ID": "P2" }, "ID": "4", "Amount": 8, "per": "Customer" }, { "Customer": { "ID": "C3" }, "Product": { "ID": "P1" }, "ID": "6", "Amount": 2, "per": "Customer" }, { "Customer": { "ID": "C3" }, "Product": { "ID": "P1" }, "ID": "6", "Amount": 2, "per": "Product" }, { "Customer": { "ID": "C2" }, "Product": { "ID": "P2" }, "ID": "4", "Amount": 8, "per": "Product" }, { "Customer": { "ID": "C2" }, "Product": { "ID": "P3" }, "ID": "5", "Amount": 4, "per": "Product" } ] }
7.7 Model Functions as Set Transformations Example 85: As a variation of example 82, a query for returning the best-selling product per country and the total amount of the remaining products can be formulated with the help of a model function. For this purpose, the model includes a definition of a TopCountAndRemainder function that accepts a count and a numeric property for the top entities: odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 56 of 69
Standards Track Work Product
<edm:Function Name="TopCountAndRemainder" IsBound="true"> <edm:Parameter Name="EntityCollection" Type="Collection(Edm.EntityType)" /> <edm:Parameter Name="Count" Type="Edm.Int16" /> <edm:Parameter Name="Property" Type="Edm.String" /> <edm:ReturnType Type="Collection(Edm.EntityType)" /> </edm:Function> The function retains those entities that topcount also would retain, and replaces the remaining entities by a single aggregated entity, where only the numeric property has a value, which is the sum over those remaining entities: GET /service/Sales?$apply= groupby((Customer/Country,Product/Name), aggregate(Amount with sum as Total)) /groupby((Customer/Country), Self.TopCountAndRemainder(Count=1,Property='Total')) results in { "@context": "$metadata#Sales(Customer(Country),Total)", "value": [ { "Customer": { "Country": "Netherlands" }, "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 3 }, { "Customer": { "Country": "Netherlands" }, "Total@type": "Decimal", "Total": 2 }, { "Customer": { "Country": "USA" }, "Product": { "Name": "Coffee" }, "Total@type": "Decimal", "Total": 12 }, { "Customer": { "Country": "USA" }, "Total@type": "Decimal", "Total": 7 } ] } Note that these two entities get their values for the Country property from the groupby transformation, which ensures that they contain all grouping properties with the correct values.
7.8 Controlling Aggregation per Rollup Level For a leveled hierarchy, consumers may specify a different aggregation method per level as a hierarchy level below the root level. Example 86: get the average of the overall amount by month per product. Using a transformation sequence: GET /service/Sales?$apply=groupby((Product/ID,Product/Name,Time/Month), aggregate(Amount with sum) as Total)) /groupby((Product/ID,Product/Name), aggregate(Total with average as MonthlyAverage))
7.9 Aggregation in Recursive Hierarchies ⚠ Example 87: The input set Sales is filtered along a hierarchy on a related entity (navigation property SalesOrganization) before an aggregation GET /service/Sales?$apply= descendants($root/SalesOrganizations, SalesOrgHierarchy, SalesOrganization/ID, filter(SalesOrganization/Name eq 'US'),
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 57 of 69
Standards Track Work Product
keep start) /aggregate(Amount with sum as TotalAmount) The same aggregate value is computed if the input set is the hierarchical entity SalesOrganizations and an assumed partner navigation property Sales of SalesOrganization appears in the aggregate transformation GET /service/SalesOrganizations?$apply= descendants($root/SalesOrganizations, SalesOrgHierarchy, ID, filter(Name eq 'US'), keep start) /aggregate(Sales/Amount with sum as TotalAmount) Example 88: Preorder traversal of a hierarchy with 1:N relationship with collection-valued segment p1 = Sales and r = SalesOrganization/ID. GET /service/Products?$apply=traverse( $root/SalesOrganizations, SalesOrgHierarchy, Sales/SalesOrganization/ID, preorder, Name asc) &$select=ID The result contains multiple instances of the same Product that differ in their Sales navigation property even though they agree in their ID key property. The node x with x/ID = "US" has σ(x) = {"Sales": [{"SalesOrganization": {"ID": "US"}}]}. { "@context": "$metadata#Products(ID,Sales(SalesOrganization(ID)))", "value": [ { "ID": "P1", "Sales": [ { "SalesOrganization": { "ID": "Sales" } } ] }, { "ID": "P2", "Sales": [ { "SalesOrganization": { "ID": "Sales" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "Sales" } } ] }, { "ID": "P1", "Sales": [ { "SalesOrganization": { "ID": "EMEA" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "EMEA" } } ] }, { "ID": "P1", "Sales": [ { "SalesOrganization": { "ID": "EMEA Central" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "EMEA Central" } } ] }, { "ID": "P1", "Sales": [ { "SalesOrganization": { "ID": "US" } } ] }, { "ID": "P2", "Sales": [ { "SalesOrganization": { "ID": "US" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "US" } } ] }, { "ID": "P2", "Sales": [ { "SalesOrganization": { "ID": "US East" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "US East" } } ] }, { "ID": "P1", "Sales": [ { "SalesOrganization": { "ID": "US West" } } ] }, { "ID": "P2", "Sales": [ { "SalesOrganization": { "ID": "US West" } } ] }, { "ID": "P3", "Sales": [ { "SalesOrganization": { "ID": "US West" } } ] } ] }
7.10 Maintaining Recursive Hierarchies Besides changes to the structural properties of the entities in a hierarchical collection, hierarchy maintenance involves changes to the parent-child relationships. Example 89: Move a sales organization Switzerland under the parent EMEA Central by binding the parent navigation property to EMEA Central [OData-JSON, section 8.5]: PATCH /service/SalesOrganizations('Switzerland') Content-Type: application/json { "Superordinate": { "@id": "SalesOrganizations('EMEA Central')" } }
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 58 of 69
Standards Track Work Product
results in 204 No Content. Deleting the parent from the sales organization Switzerland (making it a root) can be achieved either with: PATCH /service/SalesOrganizations('Switzerland') Content-Type: application/json { "Superordinate": { "@id": null } } or with: DELETE /service/SalesOrganizations('Switzerland')/Superordinate/$ref Example 90: If the parent navigation property contained a referential constraint for the key of the target [OData-CSDL, section 8.5], <EntityType Name="SalesOrganization"> <Key> <PropertyRef Name="ID" /> </Key> <Property Name="ID" Type="Edm.String" Nullable="false" /> <Property Name="Name" Type="Edm.String" /> <Property Name="SuperordinateID" Type="Edm.String" /> <NavigationProperty Name="Superordinate" Type="SalesModel.SalesOrganization"> <ReferentialConstraint Property="SuperordinateID" ReferencedProperty="ID" /> </NavigationProperty> </EntityType> then alternatively the property taking part in the referential constraint [OData-Protocol, section 11.4.8.1] could be changed to EMEA Central: PATCH /service/SalesOrganizations('Switzerland') Content-Type: application/json { "SuperordinateID": "EMEA Central" }
If the parent-child relationship between sales organizations is maintained in a separate entity set, a node can have multiple parents, with additional information on each parent-child relationship. ⚠ Example 91: Assume the relation from a node to its parent nodes contains a weight: <EntityType Name="SalesOrganizationRelation"> <Key> <PropertyRef Name="Superordinate/ID" Alias="SuperordinateID" /> </Key> <Property Name="Weight" Type="Edm.Decimal" Nullable="false" DefaultValue="1" /> <NavigationProperty Name="Superordinate" Type="SalesModel.SalesOrganization" Nullable="false" /> </EntityType> <EntityType Name="SalesOrganization"> <Key> <PropertyRef Name="ID" /> </Key> <Property Name="ID" Type="Edm.String" Nullable="false" /> <Property Name="Name" Type="Edm.String" /> <NavigationProperty Name="Relations" Type="Collection(SalesModel.SalesOrganizationRelation)" Nullable="false" ContainsTarget="true" /> <Annotation Term="Aggregation.RecursiveHierarchy" Qualifier="MultiParentHierarchy"> <Record> <PropertyValue Property="NodeProperty" PropertyPath="ID" />
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 59 of 69
Standards Track Work Product
<PropertyValue Property="ParentNavigationProperty" NavigationPropertyPath="Relations/Superordinate" /> </Record> </Annotation> </EntityType> Further assume the following relationships between sales organizations: ID
Relations/SuperordinateID
US
Sales
Relations/Weight 1
EMEA
Sales
1
EMEA Central
EMEA
Atlantis
US
0.6
Atlantis
EMEA
0.4
Phobos
Mars
1
1
Then Atlantis is a node with two parents. The standard hierarchical transformations ancestors and descendants disregard the weight property and consider both parents equally valid. Transformation traverse has no defined behavior. Since this example contains no referential constraint, there is no analogy to example 90. The alias SuperordinateID cannot be used in the payload, the following request is invalid: POST /service/SalesOrganizations('Mars')/Relations Content-Type: application/json { "SuperordinateID": "Sales" } The alias SuperordinateID is used in the request to delete the added relationship again: DELETE /service/SalesOrganizations('Mars')/Relations('Sales')
7.11 Transformation Sequences Applying aggregation first covers the most prominent use cases. The slightly more sophisticated question “how much money is earned with small sales” requires filtering the base set before applying the aggregation. To enable this type of question several transformations can be specified in $apply in the order they are to be applied, separated by a forward slash. Example 92: GET /service/Sales?$apply=filter(Amount le 1) /aggregate(Amount with sum as Total) means “filter first, then aggregate”, and results in { "@context": "$metadata#Sales(Total)", "value": [ { "Total@type": "Decimal", "Total": 2 } ] }
Using filter within $apply does not preclude using it as a normal system query option. Example 93: GET /service/Sales?$apply=filter(Amount le 2)/groupby((Product/Name), aggregate(Amount with sum as Total)) &$filter=Total ge 4 results in
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 60 of 69
Standards Track Work Product
{ "@context": "$metadata#Sales(Product(Name),Total)", "value": [ { "Product": { "Name": "Paper" }, "Total@type": "Decimal", "Total": 4 }, { "Product": { "Name": "Sugar" }, "Total@type": "Decimal", "Total": 4 } ] }
For further examples, consider another data model containing entity sets for cities, countries and continents and the obvious associations between them. Example 94: getting the population per country with GET /service/Cities?$apply=groupby((Continent/Name,Country/Name), aggregate(Population with sum as TotalPopulation)) results in { "@context": "$metadata#Cities(Continent(Name),Country(Name), TotalPopulation)", "value": [ { "Continent": { "Name": "Asia" }, "Country": { "Name": "China" }, "TotalPopulation@type": "Int32", "TotalPopulation": 1412000000 }, { "Continent": { "Name": "Asia" }, "Country": { "Name": "India" }, "TotalPopulation@type": "Int32", "TotalPopulation": 1408000000 }, … ] } Example 95: all countries with megacities and their continents GET /service/Cities?$apply=filter(Population ge 10000000) /groupby((Continent/Name,Country/Name), aggregate(Population with sum as TotalPopulation)) Example 96: all countries with tens of millions of city dwellers and the continents only for these countries GET /service/Cities?$apply=groupby((Continent/Name,Country/Name), aggregate(Population with sum as CountryPopulation)) /filter(CountryPopulation ge 10000000) /concat(identity, groupby((Continent/Name), aggregate(CountryPopulation with sum as TotalPopulation))) or GET /service/Cities?$apply=groupby((Continent/Name,Country/Name), aggregate(Population with sum as CountryPopulation)) /filter(CountryPopulation ge 10000000) /concat(groupby((Continent/Name,Country/Name), aggregate(CountryPopulation with sum as TotalPopulation)), groupby((Continent/Name), aggregate(CountryPopulation with sum as TotalPopulation))) Example 97: all countries with tens of millions of city dwellers and all continents with cities independent of their size GET /service/Cities?$apply=groupby((Continent/Name,Country/Name), aggregate(Population with sum as CountryPopulation)) odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 61 of 69
Standards Track Work Product
/concat(filter(CountryPopulation ge 10000000), groupby((Continent/Name), aggregate(CountryPopulation with sum as TotalPopulation))) Example 98: assuming that Amount is a custom aggregate in addition to the property, determine the total for countries with an Amount greater than 1000 GET /service/SalesOrders?$apply= groupby((Customer/Country),aggregate(Amount)) /filter(Amount gt 1000) /aggregate(Amount)
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 62 of 69
Standards Track Work Product
8 Conformance Conforming services MUST follow all rules of this specification for the set transformations and aggregation methods they support. They MUST implement all set transformations and aggregation methods they advertise via the annotation ApplySupported. Conforming clients MUST be prepared to consume a model that uses any or all of the constructs defined in this specification, including custom aggregation methods defined by the service, and MUST ignore any constructs not defined in this version of the specification.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 63 of 69
Standards Track Work Product
Appendix A. References This appendix contains the normative references that are used in this document. While any hyperlinks included in this appendix were valid at the time of publication, OASIS cannot guarantee their longterm validity.
A.1 Normative References The following documents are referenced in such a way that some or all of their content constitutes requirements of this document. [OData-ABNF] ABNF components: OData ABNF Construction Rules Version 4.01 and OData ABNF Test Cases. See link in “Related work” section on cover page. [OData-Agg-ABNF] OData Aggregation ABNF Construction Rules Version 4.0. See link in “Additional artifacts” section on cover page. [OData-CSDL] OData Common Schema Definition Language (CSDL) JSON Representation Version 4.01. See link in “Related work” section on cover page. OData Common Schema Definition Language (CSDL) XML Representation Version 4.01. See link in “Related work” section on cover page. [OData-JSON] OData JSON Format Version 4.01. See link in “Related work” section on cover page. [OData-Protocol] OData Version 4.01. Part 1: Protocol. See link in “Related work” section on cover page. [OData-URL] OData Version 4.01. Part 2: URL Conventions. See link in “Related work” section on cover page. [OData-VocAggr] OData Aggregation Vocabulary. See link in “Additional artifacts” section on cover page. [OData-VocCore] OData Core Vocabulary. See link in “Related work” section on cover page. [RFC2119] Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels”, BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997 https://www.rfc-editor.org/info/rfc2119.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 64 of 69
Standards Track Work Product
[RFC8174] Leiba, B., “Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words”, BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017 https://www.rfc-editor.org/info/rfc8174.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 65 of 69
Standards Track Work Product
Appendix B. Acknowledgments B.1 Special Thanks The contributions of the OASIS OData Technical Committee members, enumerated in [OData-Protocol, section C.2], are gratefully acknowledged.
B.2 Participants OData TC Members: First Name
Last Name
Company
George
Ericson
Dell
Hubert
Heijkers
IBM
Ling
Jin
IBM
Stefan
Hagen
Individual
Michael
Pizzo
Microsoft
Christof
Sprenger
Microsoft
Ralf
Handl
SAP SE
Gerald
Krause
SAP SE
Heiko
Theißen
SAP SE
Martin
Zurmuehl
SAP SE
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 66 of 69
Standards Track Work Product
Appendix C. Revision History Revision
Date
Editor
Changes Made
Working Draft 01
201211-12
Ralf Handl
Translated contribution into OASIS format
Committee Specification Draft 01
201307-25
Ralf Handl Hubert Heijkers Gerald Krause Michael Pizzo Martin Zurmuehl
Switched to pipe-and-filter-style query language based on composable set transformations Fleshed out examples and addressed numerous editorial and technical issues processed through the TC Added Conformance section
Committee Specification Draft 02
201401-09
Ralf Handl Hubert Heijkers Gerald Krause Michael Pizzo Martin Zurmuehl
Dynamic properties used all aggregated values either via aliases or via custom aggregates Refactored annotations
Committee Specification Draft 03
201507-16
Ralf Handl Hubert Heijkers Gerald Krause Michael Pizzo Martin Zurmuehl
Added compute transformation Minor clean-up
Committee Specification Draft 04
202307-05
Ralf Handl Hubert Heijkers Gerald Krause Michael Pizzo Heiko Theißen
Added section about fundamentals of input and output sets Algorithmic descriptions of transformations Added join and outerjoin transformations, replaced expand by addnested Added transformations orderby, skip, top, nest Added transformations for recursive hierarchies, updated related filter functions Added functions evaluable on a collection, introduced keyword $these Merged section 4 “Representation of Aggregated Instances” into section 3 Remove actions and functions (except set transformations) on aggregated entities, adapted section “Actions and Functions on Aggregated Entities”
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 67 of 69
Standards Track Work Product
Revision
Date
Editor
Changes Made
Committee Specification 03
202309-19
Ralf Handl Gerald Krause Heiko Theißen
Non-material changes from public review feedback
Committee Specification Draft 05
202510-01
Gerald Krause Heiko Theißen
Remove sections not intended for OASIS Standard
Committee Specification 04
202511-18
Gerald Krause Heiko Theißen
No changes from public review
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 68 of 69
Standards Track Work Product
Appendix D. Notices Copyright © OASIS Open 2025. All Rights Reserved. All capitalized terms in the following text have the meanings assigned to them in the OASIS Intellectual Property Rights Policy (the “OASIS IPR Policy”). The full Policy may be found at the OASIS website. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published, and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this section are included on all such copies and derivative works. However, this document itself may not be modified in any way, including by removing the copyright notice or references to OASIS, except as needed for the purpose of developing any document or deliverable produced by an OASIS Technical Committee (in which case the rules applicable to copyrights, as set forth in the OASIS IPR Policy, must be followed) or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by OASIS or its successors or assigns. This document and the information contained herein is provided on an “AS IS” basis and OASIS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY OWNERSHIP RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. As stated in the OASIS IPR Policy, the following three paragraphs in brackets apply to OASIS Standards Final Deliverable documents (Committee Specification, Candidate OASIS Standard, OASIS Standard, or Approved Errata). [OASIS requests that any OASIS Party or any other party that believes it has patent claims that would necessarily be infringed by implementations of this OASIS Standards Final Deliverable, to notify OASIS TC Administrator and provide an indication of its willingness to grant patent licenses to such patent claims in a manner consistent with the IPR Mode of the OASIS Technical Committee that produced this deliverable.] [OASIS invites any party to contact the OASIS TC Administrator if it is aware of a claim of ownership of any patent claims that would necessarily be infringed by implementations of this OASIS Standards Final Deliverable by a patent holder that is not willing to provide a license to such patent claims in a manner consistent with the IPR Mode of the OASIS Technical Committee that produced this OASIS Standards Final Deliverable. OASIS may include such claims on its website, but disclaims any obligation to do so.] [OASIS takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this OASIS Standards Final Deliverable or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on OASIS’ procedures with respect to rights in any document or deliverable produced by an OASIS Technical Committee can be found on the OASIS website. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this OASIS Standards Final Deliverable, can be obtained from the OASIS TC Administrator. OASIS makes no representation that any information or list of intellectual property rights will at any time be complete, or that any claims in such list are, in fact, Essential Claims.] The name “OASIS” is a trademark of OASIS, the owner and developer of this specification, and should be used only to refer to the organization and its official outputs. OASIS welcomes reference to, and implementation and use of, specifications, while reserving the right to enforce its marks against misleading uses. Please see https://www.oasisopen.org/policies-guidelines/trademark/ for above guidance.
odata-data-aggregation-ext-v4.0-cs04
Copyright © OASIS Open 2025. All Rights Reserved.
18 November 2025 - Page 69 of 69