SPARQL 1.2 Federated Query W3C Working Draft 23 April 2026 More details about this document This version: https://www.w3.org/TR/2026/WD-sparql12-federated-query-20260423/ Latest published version: https://www.w3.org/TR/sparql12-federated-query/ Latest editor's draft: https://w3c.github.io/sparql-federated-query/spec/ History: https://www.w3.org/standards/history/sparql12-federated-query/ Commit history Test suite: https://w3c.github.io/rdf-tests/ Latest Recommendation: https://www.w3.org/TR/2013/REC-sparql11-federated-query-20130321 Editors: Ruben Taelman Gregory Williams Former editors: Eric Prud'hommeaux Carlos Buil-Aranda Feedback: GitHub w3c/sparql-federated-query ( pull requests , new issue , open issues ) [email protected] with subject line [sparql12-federated-query] … message topic … ( archives ) Copyright © 2012-2026 World Wide Web Consortium . W3C ® liability , trademark and permissive document license rules apply. Abstract RDF is a directed, labeled graph data model for representing information in the Web. SPARQL can be used to express queries across diverse data sources, whether the data is stored natively as RDF or viewed as RDF via middleware. This specification defines the syntax and semantics of SPARQL Federated Query extension for executing queries distributed over different SPARQL endpoints. The SERVICE keyword extends SPARQL to support queries that merge data distributed across the Web. Status of This Document This section describes the status of this document at the time of its publication. A list of current W3C publications and the latest revision of this technical report can be found in the W3C standards and drafts index . This specification is published by the RDF Star Working Group as part of the update of specifications for format and errata. This document was published by the RDF & SPARQL Working Group as a Working Draft using the Recommendation track . Publication as a Working Draft does not imply endorsement by W3C and its Members. This is a draft document and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to cite this document as other than a work in progress. Future updates to this upcoming Recommendation may incorporate new features . This document was produced by a group operating under the W3C Patent Policy . W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent that the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy . This document is governed by the 18 August 2025 W3C Process Document . Set of Documents This document is one of twelve SPARQL 1.2 documents produced by the RDF & SPARQL Working Group . List of documents SPARQL 1.2 Documents: What’s New in SPARQL 1.2 SPARQL 1.2 Concepts SPARQL 1.2 Query Language SPARQL 1.2 Update SPARQL 1.2 Service Description SPARQL 1.2 Federated Query (this document) SPARQL 1.2 Query Results JSON Format SPARQL 1.2 Query Results CSV and TSV Formats SPARQL 1.2 Query Results XML Format SPARQL 1.2 Entailment Regimes SPARQL 1.2 Protocol SPARQL 1.2 Graph Store Protocol Table of Contents Abstract Status of This Document Set of Documents 1. Introduction 1.1 Document Conventions 1.1.1 Namespaces 1.1.2 Result Descriptions 1.1.3 Terminology 2. SPARQL Federated Query Extension 2.1 Simple query to a remote SPARQL endpoint 2.2 SPARQL query with OPTIONAL to two remote SPARQL endpoints 2.3 Service Execution Failure 2.4 Interplay of SERVICE and VALUES (Informative) 3. SPARQL Simple Federation Extension: semantics 3.1 Translation to the SPARQL Algebra 3.2 SPARQL Simple Federation Extension Algebra 3.2.1 SERVICE Examples 4. SERVICE Variables (Informative) 5. Conformance 5.1 Conformance 6. Security Considerations 7. Acknowledgements A. Changes between SPARQL 1.1 Federated Query and SPARQL 1.2 Federated Query B. Privacy Considerations C. Internationalization Considerations D. Index D.1 Terms defined by this specification D.2 Terms defined by reference E. References E.1 Normative references E.2 Informative references 1. Introduction The growing number of SPARQL query services offer data consumers an opportunity to merge data distributed across the Web. This specification defines the syntax and semantics of the SERVICE extension to the SPARQL Query Language. This extension allows a query author to direct a portion of a query to a particular SPARQL endpoint. Results are returned to the federated query processor and are combined with results from the rest of the query. 1.1 Document Conventions 1.1.1 Namespaces This document uses the same namespaces as from SPARQL 1.2 Query Language . 1.1.2 Result Descriptions Result sets are illustrated in tabular form as in SPARQL 1.2 Query Language . x y z "Alice" <http://example/a> A 'binding' is a pair ( variable , RDF term ). There are three variables: x , y , and z (shown as column headers). Each solution is shown as one row in the body of the table. Here, there is a single solution, in which variable x is bound to "Alice" , variable y is bound to http://example/a , and variable z is not bound to an RDF term. Variables are not required to be bound in a solution. 1.1.3 Terminology The following terms are defined in SPARQL 1.2 Query Language and reused in this document: IRI (corresponds to the Concepts and Abstract Syntax term RDF URI reference ) Solution Mapping Solution Sequence 2. SPARQL Federated Query Extension The SERVICE keyword instructs a federated query processor to invoke a portion of a SPARQL query against a remote SPARQL endpoint. This section presents examples of how to use the SERVICE keyword. The following sections define the syntax and semantics of this extension. 2.1 Simple query to a remote SPARQL endpoint This example shows how to query a remote SPARQL endpoint and join the returned data with the data from the local RDF Dataset. Consider a query to find the names of the people we know. Data about the names of various people is available at the http://people.example.org/sparql endpoint: @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix : <http://example.org/> .
:people15 foaf:name "Alice" . :people16 foaf:name "Bob" . :people17 foaf:name "Charles" . :people18 foaf:name "Daisy" . and one wants to combine with a local FOAF file http://example.org/myfoaf.rdf that contains the single triple: <http://example.org/myfoaf/I> <http://xmlns.com/foaf/0.1/knows> <http://example.org/people15> . Query: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name FROM <http://example.org/myfoaf.rdf> WHERE { <http://example.org/myfoaf/I> foaf:knows ?person . SERVICE <http://people.example.org/sparql> { ?person foaf:name ?name . } } This query, on the data above, has one solution: Query Result: name "Alice" 2.2 SPARQL query with OPTIONAL to two remote SPARQL endpoints Imagine we want to query people and optionally obtain their interests and the names of people they know. Imagine for instance, two endpoints containing data about people: Data in the default graph at remote SPARQL endpoint: http://people.example.org/sparql @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix : <http://example.org/> .
:people15 foaf:name "Alice" . :people16 foaf:name "Bob" . :people17 foaf:name "Charles" . :people17 foaf:interest <http://www.w3.org/2001/sw/rdb2rdf/> . and data in the default graph the remote SPARQL endpoint: http://people2.example.org/sparql @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix : <http://example.org/> .
:people15 foaf:knows :people18 . :people18 foaf:name "Mike" . :people17 foaf:knows :people19 . :people19 foaf:name "Daisy" . Query: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?person ?interest ?known WHERE { SERVICE <http://people.example.org/sparql> { ?person foaf:name ?name . OPTIONAL { ?person foaf:interest ?interest . SERVICE <http://people2.example.org/sparql> { ?person foaf:knows ?known . } } } } This query, on the data above, has three solutions: Query Result: person interest known "Alice" "Bob" "Charles" <http://www.w3.org/2001/sw/rdb2rdf/> <http://example.org/people19> Notice that in the query above there is a nested SERVICE in the OPTIONAL clause. This query requires the SPARQL query service at http://people.example.org/sparql to support basic federated query. 2.3 Service Execution Failure The execution of a SERVICE pattern may fail due to several reasons: the remote service may be down, the service IRI may not be dereferenceable, or the endpoint may return an error to the query. Normally, under such circumstances the invoked query containing a SERVICE pattern fails as a whole. Queries may explicitly allow failed SERVICE requests with the use of the SILENT keyword. The SILENT keyword indicates that errors encountered while accessing a remote SPARQL endpoint should be ignored while processing the query. The failed SERVICE clause is treated as if it had a result of a single solution with no bindings. In the following query the SILENT keyword is present. If the remote SPARQL endpoint is not available because the SPARQL endpoint does not exist, it is down or it is not accessible the query will return a solution sequence of one empty solution mapping. If the SILENT keyword is not present, the query will stop and return the error. Data in <http://people.example.org/sparql> endpoint: <http://example.org/people15> <http://xmlns.com/foaf/0.1/name> "Charles" . Query: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?name WHERE { SERVICE SILENT <http://people.example.org/sparql> { <http://example.org/people15> foaf:name ?name . } } Query result if an error occurs while querying the remote SPARQL endpoint: name 2.4 Interplay of SERVICE and VALUES (Informative) SPARQL Query includes the VALUES clause ( VALUES ), which can be used to provide an unordered solution sequence that is joined with the results of the query evaluation. Implementers of SPARQL Federated Query may use the VALUES clause to constrain the results received from a remote endpoint based on solution bindings from evaluating other parts of the query. The following example shows how SERVICE and VALUES can work together. Suppose a query that asks for all instances of foaf:Person in the default graph and also their known people in the remote endpoint http://example.org/sparql : Data in the default graph: @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix : <http://example.org/> .
:a a foaf:Person ; foaf:name "Alan" ; foaf:mbox; "[email protected]" . :b a foaf:Person ; foaf:name "Bob" ; foaf:mbox "[email protected]" . and data in the default graph the remote SPARQL endpoint http://example.org/sparql : @prefix foaf: <http://xmlns.com/foaf/0.1/> . @prefix : <http://example.org/> .
:a foaf:knows :b . :b foaf:knows :c . :c foaf:knows :a . :a foaf:interest "SPARQL Basic Federated Query" . :b foaf:interest "SPARQL Query" . :c foaf:interest "RDB2RDF Direct mapping" . Query: PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?s { ?s a foaf:Person . SERVICE <http://example.org/sparql> {?s foaf:knows ?o } } When the original query is executed naively, with an unconstrained service call the endpoint may return more results than necessary. It may also happen that the SPARQL endpoint will not return all of them. Many existing SPARQL endpoints have restrictions in the number of results they return and may miss the ones matching subjects ?s from the local default graph. Thus, an implementation of a query planner for federated queries may decide to decompose the query into two queries instead, where first the bindings from the local default graph are evaluated: Query: PREFIX : <http://example.org/> PREFIX foaf: <http://xmlns.com/foaf/0.1/> SELECT ?s { ?s a foaf:Person } This query, on the data above, has two solutions: Query Result: s <http://example.org/a> <http://example.org/b> Next, dispatch to the remote endpoint <http://example.org/sparql> a constrained query with the solutions for ?s : PREFIX foaf: <http://xmlns.com/foaf/0.1/> PREFIX : <http://example.org/> SELECT * {?s foaf:knows ?o } VALUES (?s) { (:a) (:b) } This query on <http://example.org/sparql> has two solutions: Query Result: s o <http://example.org/a> <http://example.org/b> <http://example.org/b> <http://example.org/c> Both intermediary solution sequences can now be joined together, and projected to the requested variables to get to the expected two solution mappings for the overall query: s <http://example.org/a> <http://example.org/b> 3. SPARQL Simple Federation Extension: semantics 3.1 Translation to the SPARQL Algebra The SERVICE extension is defined as an additional type of GroupGraphPattern, with an accompanying addition to SPARQL Query's Transform (syntax form) : If the form is GroupGraphPattern From the Translate Graph Patterns section of SPARQL 1.2 Query Language we extend the transformation of GroupGraphPattern to define the transformation of SERVICE patterns: Let FS := the empty set Let G := the empty pattern, Z, a basic graph pattern which is the empty set. Let SilentOp := boolean, indicating SERVICE error behavior.
For each element E in the GroupGraphPattern If E is of the form FILTER(expr) FS := FS ∪ {expr} End
If E is of the form OPTIONAL{P} Let A := Transform(P) If A is of the form Filter(F, A2) G := LeftJoin(G, A2, F) Else G := LeftJoin(G, A, true) End End
If E is of the form MINUS{P} G := Minus(G, Transform(P)) End
If E is of the form BIND(expr AS var) G := Extend(G, var, expr) End
If E is any other form Let A := Transform(E) G := Join(G, A) End
If E is of the form SERVICE [SILENT] IRI {P} Let G := Join(G, Service(IRI, Transform(P), SilentOp)) End End If FS is not empty: Let X := Conjunction of expressions in FS G := Filter(X, G)
The result is G. 3.2 SPARQL Simple Federation Extension Algebra The evaluation of SERVICE is defined in terms of the SPARQL 1.2 Query Results XML Format returned by a SPARQL 1.2 Protocol execution of the nested graph pattern: Definition: Evaluation of a Service Pattern Let iri be an IRI, Ω 0 the solution set with one empty solution, and SilentOp be a boolean variable to indicate that SERVICE execution should ignore errors when true. then: eval(D(G), Service(IRI,P,SilentOp)) = Invocation( iri, P, SilentOp ) where: Invocation(IRI, P, SilentOp) is the multiset of solution mappings corresponding to the results of executing query SELECT * WHERE Q against the service endpoint with IRI iri where Q is the serialization of P in SPARQL syntax, in case of a successful service invocation according to the SPARQL protocol, and otherwise Ω 0 . in case SilentOp is true, and otherwise error. 3.2.1 SERVICE Examples In the folowing section we introduce two examples showing the evaluation of SERVICE patterns in the SPARQL algebra: Example: a SERVICE graph pattern in a series of joins: ... WHERE { { ?s :p1 ?v1 } SERVICE <srvc> {?s :p2 ?v2 } { ?s :p3 ?v2 } } Join( Service( <srvc>, BGP( ?s :p2 ?v2 ), false ), BGP( ?s :p3 ?v2 ) ) Example: a SERVICE SILENT graph pattern in a series of joins: ... WHERE { { ?s :p1 ?v1 } SERVICE SILENT <srvc> {?s :p2 ?v2 } { ?s :p3 ?v2 } } Join( Service( <srvc>, BGP( ?s :p2 ?v2 ), true ), BGP( ?s :p3 ?v2 ) ) 4. SERVICE Variables (Informative) In the this section we do not present official evaluation semantics for the SPARQL pattern SERVICE VAR . We only provide indications about how the evaluation of the SPARQL pattern SERVICE VAR can be evaluated. A variable used in place of a service IRI indicates that the service call for any solution depends on that variable's binding in that solution. For instance, the default graph may contain data about which services contain data about project endpoints. We assume the following data on various projects that contains information about SPARQL endpoints where data about these projects (using the DOAP vocabulary ) can be queried from: @prefix void: <http://rdfs.org/ns/void#> . @prefix dc: <http://purl.org/dc/elements/1.1/> . @prefix doap: <http://usefulinc.com/ns/doap#> .
[] dc:subject "Querying RDF" ; void:sparqlEndpoint <http://projects1.example.org/sparql> . [] dc:subject "Querying RDF remotely" ; void:sparqlEndpoint <http://projects2.example.org/sparql> . [] dc:subject "Updating RDF remotely" ; void:sparqlEndpoint <http://projects3.example.org/sparql> . Data in the default graph at remote SPARQL endpoint http://projects2.example.org/sparql: _:project1 doap:name "Query remote RDF Data" . _:project1 doap:created "2011-02-12"^^xsd:date . _:project2 doap:name "Querying multiple SPARQL endpoints" . _:project2 doap:created "2011-02-13"^^xsd:date . Data in the default graph at remote SPARQL endpoint http://projects3.example.org/sparql: _:project3 doap:name "Update remote RDF Data" . _:project3 doap:created "2011-02-14"^^xsd:date . We now want to query the project names of projects on the subject "remote": PREFIX void: <http://rdfs.org/ns/void#> PREFIX dc: <http://purl.org/dc/elements/1.1/> PREFIX doap: <http://usefulinc.com/ns/doap#>
SELECT ?service ?projectName WHERE { # Find the service with subject "remote". ?p dc:subject ?projectSubject ; void:sparqlEndpoint ?service . FILTER regex(?projectSubject, "remote")
# Query that service projects. SERVICE ?service { ?project doap:name ?projectName . } } In the following table we present the intuitive solutions for this query with the data above: Query Result: service projectName <http://projects2.example.org/sparql> "Query remote RDF Data" <http://projects2.example.org/sparql> "Querying multiple SPARQL endpoints" <http://projects3.example.org/sparql> "Update remote RDF Data" A SERVICE clause involving a variable can be executed as a series of separate invocations of SPARQL query services. The results of each invocation are combined using union. The query engine must determine the possible target SPARQL query services. The exact mechanism for doing this is not defined in this document. Execution order may also be used to determine the list of services to to be tried. The example above suggests a specific order of execution: evaluating the basic graph pattern and filter outside the SERVICE block first will yield bindings for ?service which may then be used to evaluate the SERVICE block: ?p dc:subject ?projectSubject ; void:sparqlEndpoint ?service FILTER regex(?projectSubject, "remote") Once ?service has been evaluated it is possible to execute SERVICE for each value of ?service : SERVICE ?service { ?project doap:name ?projectName . } Note that blank nodes are unique to any document which serializes them. Also, SERVICE calls depend on the SPARQL 1.2 Protocol which transfers serialized RDF documents making blank nodes unique between service calls. 5. Conformance As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative. The key word OPTIONAL in this document is to be interpreted as described in BCP 14 [ RFC2119 ] [ RFC8174 ] when, and only when, it appears in all capitals, as shown here. 5.1 Conformance See section 4 SPARQL Federated Query Grammar regarding conformance of SPARQL Query strings that include the SPARQL Federated Query Extensions. See section 3.1 Definition of SERVICE for conformance of query results for the SERVICE keyword. This specification is intended for use in conjunction with the SPARQL 1.2 Query Language . See that specification for its conformance criteria. 6. Security Considerations SPARQL queries using SERVICE imply that a URI will be dereferenced, and that the result will be incorporated into a working data set. All of the security issues of SPARQL Protocol , SPARQL Query , and Uniform Resource Identifier (URI): Generic Syntax Section 7 should be considered. 7. Acknowledgements The SPARQL Federated Query document is a product of the whole of the W3C SPARQL Working Group , and our thanks for discussions, comments, and reviews go to all present and past members. In addition, we have had comments and discussions with many people through the working group comments list. All comments go to making a better document. Carlos would also like to particularly thank Jorge Pérez, Oscar Corcho, and Marcelo Arenas for their discussions on the syntax and semantics of the Federated Query extension. A. Changes between SPARQL 1.1 Federated Query and SPARQL 1.2 Federated Query This section is non-normative. Refer to RDF as a data model instead of data format in Abstract errata-fq-1 : Incorrect example in interplay of SERVICE and VALUES example Update mentions on SPARQL and RDF 1.1 to 1.2. B. Privacy Considerations TODO C. Internationalization Considerations TODO D. Index D.1 Terms defined by this specification D.2 Terms defined by reference [ RDF12-CONCEPTS ] defines the following: IRI RDF term [ RFC3986 ] defines the following: Uniform Resource Identifier (URI): Generic Syntax Section 7 [ SPARQL12-PROTOCOL ] defines the following: SPARQL Protocol [ SPARQL12-QUERY ] defines the following: GroupGraphPattern Solution Mapping Solution Sequence SPARQL Federated Query Grammar SPARQL Query SPARQL Query strings Transform (syntax form) Translate Graph Patterns section VALUES variable E. References E.1 Normative references [RDF12-CONCEPTS] RDF 1.2 Concepts and Abstract Data Model . Andy Seaborne; Gregg Kellogg; Olaf Hartig; Pierre-Antoine Champin. W3C. 7 April 2026. W3C Candidate Recommendation. URL: https://www.w3.org/TR/rdf12-concepts/ [RFC2119] Key words for use in RFCs to Indicate Requirement Levels . S. Bradner. IETF. March 1997. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc2119 [rfc3986] Uniform Resource Identifier (URI): Generic Syntax . T. Berners-Lee; R. Fielding; L. Masinter. IETF. January 2005. Internet Standard. URL: https://www.rfc-editor.org/rfc/rfc3986 [RFC8174] Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words . B. Leiba. IETF. May 2017. Best Current Practice. URL: https://www.rfc-editor.org/rfc/rfc8174 [SPARQL12-PROTOCOL] SPARQL 1.2 Protocol . Andy Seaborne; Ruben Taelman; Gregory Williams; Thomas Pellissier Tanon. W3C. 14 August 2025. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-protocol/ [SPARQL12-QUERY] SPARQL 1.2 Query Language . Olaf Hartig; Andy Seaborne; Ruben Taelman; Gregory Williams; Thomas Pellissier Tanon. W3C. 16 April 2026. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-query/ E.2 Informative references [SPARQL12-CONCEPTS] SPARQL 1.2 Concepts . The W3C RDF & SPARQL Working Group. W3C. W3C Editor's Draft. URL: https://w3c.github.io/sparql-concepts/spec/ [SPARQL12-ENTAILMENT] SPARQL 1.2 Entailment Regimes . Peter Patel-Schneider. W3C. 9 April 2026. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-entailment/ [SPARQL12-GRAPH-STORE-PROTOCOL] SPARQL 1.2 Graph Store Protocol . Andy Seaborne; Thomas Pellissier Tanon. W3C. 19 December 2024. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-graph-store-protocol/ [SPARQL12-NEW] What’s New in SPARQL 1.2 . The W3C RDF & SPARQL Working Group. W3C. W3C Editor's Draft. URL: https://w3c.github.io/sparql-new/spec/ [SPARQL12-RESULTS-CSV-TSV] SPARQL 1.2 Query Results CSV and TSV Formats . Ruben Taelman; Gregory Williams; Thomas Pellissier Tanon. W3C. 28 March 2026. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-results-csv-tsv/ [SPARQL12-RESULTS-JSON] SPARQL 1.2 Query Results JSON Format . Andy Seaborne; Ruben Taelman; Gregory Williams; Thomas Pellissier Tanon. W3C. 28 March 2026. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-results-json/ [SPARQL12-RESULTS-XML] SPARQL 1.2 Query Results XML Format . Ruben Taelman; Dominik Tomaszuk; Thomas Pellissier Tanon. W3C. 27 December 2024. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-results-xml/ [SPARQL12-SERVICE-DESCRIPTION] SPARQL 1.2 Service Description . Ruben Taelman; Gregory Williams. W3C. 19 March 2026. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-service-description/ [SPARQL12-UPDATE] SPARQL 1.2 Update . Ruben Taelman; Andy Seaborne; Thomas Pellissier Tanon. W3C. 14 August 2025. W3C Working Draft. URL: https://www.w3.org/TR/sparql12-update/ ↑ Permalink Referenced in: § 1.1.3 Terminology Permalink Referenced in: § 1.1.2 Result Descriptions Permalink Referenced in: § 6. Security Considerations Permalink Referenced in: § 6. Security Considerations Permalink Referenced in: § 3.1 Translation to the SPARQL Algebra Permalink Referenced in: § 1.1.3 Terminology Permalink Referenced in: § 1.1.3 Terminology Permalink Referenced in: § 5.1 Conformance Permalink Referenced in: § 6. Security Considerations Permalink Referenced in: § 5.1 Conformance Permalink Referenced in: § 3.1 Translation to the SPARQL Algebra Permalink Referenced in: § 3.1 Translation to the SPARQL Algebra Permalink Referenced in: § 2.4 Interplay of SERVICE and VALUES (Informative) Permalink Referenced in: § 1.1.2 Result Descriptions