This document is one of twelve SPARQL 1.2 documents produced by theRDF-star Working Group.

Unless otherwise noted in the section heading, all sections and appendices in this document are normative.

This section of the document,section 1, introduces the SPARQL Query Language specification. It presents the organization of this specification document and the conventions used throughout the specification.

Section 2 of the specification introduces the SPARQL query language itself via a series of example queries and query results.Section 3 continues the introduction of the SPARQL query language with more examples that demonstrate SPARQL's ability to express constraints on the RDF terms that appear in a query's results.

Section 4 presents details of the SPARQL query language's syntax. It is a companion to the full grammar of the language and defines how grammatical constructs represent IRIs, blank nodes, literals, and variables. Section 4 also defines the meaning of several grammatical constructs that serve as syntactic sugar for more verbose expressions.

Section 5 introduces basic graph patterns and group graph patterns, the building blocks from which more complex SPARQL query patterns are constructed. Sections 6, 7, and 8 present constructs that combine SPARQL graph patterns into larger graph patterns. In particular,Section 6 introduces the ability to make portions of a query optional;Section 7 introduces the ability to express the disjunction of alternative graph patterns; andSection 8 introduces patterns to test for the absense of information.

Section 9 adds property paths to graph pattern matching, giving a compact representation of queries and also the ability to match arbitrary length paths in the graph.

Section 10 describes the forms of assignment possible in SPARQL.

Sections 11 introduces the mechanism to group and aggregate results, which can be incorporated as subqueries as described inSection 12.

Section 13 introduces the ability to constrain portions of a query to particular source graphs. Section 13 also presents SPARQL's mechanism for defining the source graphs for a query.

Section 14 refers to the separate documentSPARQL 1.1 Federated Query.

Section 15 defines the constructs that affect the solutions of a query by ordering, slicing, projecting, limiting, and removing duplicates from a sequence of solutions.

Section 16 defines the four types of SPARQL queries that produce results in different forms.

Section 17 defines SPARQL's extensible value testing and expression framework. It presents the functions and operators that can be used to constrain the values that appear in a query's results and also calculate new values to be returned by a query.

Section 18 is a formal definition of the evaluation of SPARQL graph patterns and solution modifiers.

Section 19 contains the normative definition of the syntax for the SPARQL query andSPARQL 1.1 Update languages, as given by a grammar expressed in EBNF notation.

The example below shows a SPARQL query to find the title of a book from the given data graph. The query consists of two parts: theSELECT clause identifies the variables to appear in the query results, and theWHERE clause provides the basic graph pattern to match against the data graph. The basic graph pattern in this example consists of a single triple pattern with a single variable (?title) in the object position.

<http://example.org/book/book1> <http://purl.org/dc/elements/1.1/title> "SPARQL Tutorial" .

SELECT ?titleWHERE{    <http://example.org/book/book1> <http://purl.org/dc/elements/1.1/title> ?title .}

The result of a query is asolution sequence, corresponding to the ways in which the query's graph pattern matches the data. There may be zero, one or multiple solutions to a query.

Data:

PREFIX foaf:  <http://xmlns.com/foaf/0.1/> ._:a  foaf:name   "Johnny Lee Outlaw" ._:a  foaf:mbox   <mailto:jlow@example.com> ._:b  foaf:name   "Peter Goodguy" ._:b  foaf:mbox   <mailto:peter@example.org> ._:c  foaf:mbox   <mailto:carol@example.org> .

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE{ ?x foaf:name ?name .  ?x foaf:mbox ?mbox }

Each solution gives one way in which the selected variables can be bound to RDF terms so that the query pattern matches the data. The result set gives all the possible solutions. In the above example, the following two subsets of the data provided the two matches.

_:a foaf:name  "Johnny Lee Outlaw" ._:a foaf:box   <mailto:jlow@example.com> .

_:b foaf:name  "Peter Goodguy" ._:b foaf:box   <mailto:peter@example.org> .

This is abasic graph pattern match; all the variables used in the query pattern must be bound in every solution.

The data below contains three RDF literals:

PREFIX dt:   <http://example.org/datatype#>PREFIX ns:   <http://example.org/ns#>PREFIX :     <http://example.org/ns#>PREFIX xsd:  <http://www.w3.org/2001/XMLSchema#>:x   ns:p     "cat"@en .:y   ns:p     "42"^^xsd:integer .:z   ns:p     "abc"^^dt:specialDatatype .

This RDF data is the data graph for the query examples in sections 2.3.1–2.3.3.

SELECT ?v WHERE { ?v ?p "cat" }

SELECT ?v WHERE { ?v ?p "cat"@en }

SELECT ?v WHERE { ?v ?p 42 }

SELECT ?v WHERE { ?v ?p "abc"^^<http://example.org/datatype#specialDatatype> }

Query results can contain blank nodes. Blank nodes in the example result sets in this document are written in the form "_:" followed by ablank node identifier.

Blank node identifiers are scoped to a result set (see "SPARQL Query Results XML Format (Second Edition)" and "SPARQL 1.1 Query Results JSON Format") or, for theCONSTRUCT query form, the result graph. Use of the same identifier within a result set indicates the same blank node.

PREFIX foaf:  <http://xmlns.com/foaf/0.1/>_:a  foaf:name   "Alice" ._:b  foaf:name   "Bob" .

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT ?x ?nameWHERE  { ?x foaf:name ?name }

These two results have the same information: the blank nodes used to match the query are different in the two solutions. There need not be any relation between a blank node identifier_:a in the result set and a blank node identifier used in the syntax for the data.

An application writer should not expect blank node identifiers in a query to refer to a particular blank node in the data.

SPARQL 1.2 allows values to be created from complex expressions. The queries below show how theCONCAT function can be used to concatenate first names and last names from FOAF data, then assign the value using anexpression in theSELECT clause and also assign the value by using theBIND form.

PREFIX foaf:  <http://xmlns.com/foaf/0.1/>            _:a  foaf:givenName   "John" ._:a  foaf:surname  "Doe" .

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT ( CONCAT(?G, " ", ?S) AS ?name )WHERE  { ?P foaf:givenName ?G ; foaf:surname ?S }

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE  {     ?P foaf:givenName ?G ;        foaf:surname ?S     BIND(CONCAT(?G, " ", ?S) AS ?name)}

SPARQL has severalquery forms. TheSELECT query form returns variable bindings. TheCONSTRUCT query form returns an RDF graph. The graph is built based on a template which is used to generate RDF triples based on the results of matching the graph pattern of the query.

PREFIX org:    <http://example.com/ns#>_:a  org:employeeName   "Alice" ._:a  org:employeeId     12345 ._:b  org:employeeName   "Bob" ._:b  org:employeeId     67890 .

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>PREFIX org:    <http://example.com/ns#>CONSTRUCT { ?x foaf:name ?name }WHERE  { ?x org:employeeName ?name }

PREFIX foaf: <http://xmlns.com/foaf/0.1/>                _:x foaf:name "Alice" ._:y foaf:name "Bob" .

<rdf:RDF   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"   xmlns:foaf="http://xmlns.com/foaf/0.1/" >  <rdf:Description>    <foaf:name>Alice</foaf:name>  </rdf:Description>  <rdf:Description>    <foaf:name>Bob</foaf:name>  </rdf:Description></rdf:RDF>

SPARQLFILTER functions likeregex can test RDF literals.regex matches onlystring literals.regex can be used to match the lexical forms of other literals by using thestr function.

Query:

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>SELECT  ?titleWHERE   {     ?x dc:title ?title    FILTER regex(?title, "^SPARQL") }

Regular expression matches may be made case-insensitive with the "i" flag.

Query:

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>SELECT  ?titleWHERE   {     ?x dc:title ?title    FILTER regex(?title, "web", "i" ) }

The regular expression language isdefined by XQuery and XPath Functions and Operators and is based onXML Schema Regular Expressions.

SPARQLFILTERs can restrict on arithmetic expressions.

Query:

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title ?priceWHERE   {    ?x ns:price ?price .    FILTER (?price < 30.5)    ?x dc:title ?title . }

In addition tonumeric types, SPARQL supports typesxsd:string,xsd:boolean andxsd:dateTime (seeOperand Data Types). SectionOperator Mapping describes the operators and sectionFunction Definitions the functions that can be that can be applied to RDF terms.

Triple Patterns are written as subject, predicate and object; there are abbreviated ways of writing some common triple pattern constructs.

The following examples express the same query:

PREFIX  dc: <http://purl.org/dc/elements/1.1/>SELECT  ?titleWHERE   { <http://example.org/book/book1> dc:title ?title }

PREFIX  dc: <http://purl.org/dc/elements/1.1/>PREFIX  : <http://example.org/book/>SELECT  $titleWHERE   { :book1  dc:title  $title }

BASE    <http://example.org/book/>PREFIX  dc: <http://purl.org/dc/elements/1.1/>SELECT  $titleWHERE   { <book1>  dc:title  ?title }

?x  foaf:name  ?name ;foaf:mbox  ?mbox .

?x  foaf:name  ?name .?x  foaf:mbox  ?mbox .

?x foaf:nick  "Alice" , "Alice_" .

?x  foaf:nick  "Alice" .?x  foaf:nick  "Alice_" .

?x  foaf:name ?name ; foaf:nick  "Alice" , "Alice_" .

?x  foaf:name  ?name .?x  foaf:nick  "Alice" .?x  foaf:nick  "Alice_" .

(1 ?x 3 4) :p "w" .

_:b0  rdf:first  1 ;      rdf:rest   _:b1 ._:b1  rdf:first  ?x ;      rdf:rest   _:b2 ._:b2  rdf:first  3 ;      rdf:rest   _:b3 ._:b3  rdf:first  4 ;      rdf:rest   rdf:nil ._:b0  :p         "w" .

(1 [:p :q] ( 2 ) ) .

_:b0  rdf:first  1 ;      rdf:rest   _:b1 ._:b1  rdf:first  _:b2 ._:b2  :p         :q ._:b1  rdf:rest   _:b3 ._:b3  rdf:first  _:b4 ._:b4  rdf:first  2 ;      rdf:rest   rdf:nil ._:b3  rdf:rest   rdf:nil .

?x  a  :Class1 .[ a :appClass ] :p "v" .

?x    rdf:type  :Class1 ._:b0  rdf:type  :appClass ._:b0  :p        "v" .

Basic graph patterns are sets of triple patterns. SPARQL graph pattern matching is defined in terms of combining the results from matching basic graph patterns.

A sequence of triple patterns, with optional filters, comprises a single basic graph pattern. Any other graph pattern terminates a basic graph pattern.

In a SPARQL query string, a group graph pattern is delimited with braces:{}. For example, this query's query pattern is a group graph pattern of one basic graph pattern.

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE  {    ?x foaf:name ?name .    ?x foaf:mbox ?mbox .}

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE  {    { ?x foaf:name ?name . }   { ?x foaf:mbox ?mbox . }}

{ }

SELECT ?xWHERE {}

{  ?x foaf:name ?name .   ?x foaf:mbox ?mbox .   FILTER regex(?name, "Smith")}

{  FILTER regex(?name, "Smith")   ?x foaf:name ?name .   ?x foaf:mbox ?mbox .}

{  ?x foaf:name ?name .   FILTER regex(?name, "Smith")   ?x foaf:mbox ?mbox .}

{ ?x foaf:name ?name .  ?x foaf:mbox ?mbox .}

{  ?x foaf:name ?name . FILTER regex(?name, "Smith")  ?x foaf:mbox ?mbox .}

{  ?x foaf:name ?name .  {}  ?x foaf:mbox ?mbox .}

Optional parts of the graph pattern may be specified syntactically with theOPTIONAL keyword applied to a graph pattern:

pattern OPTIONAL {pattern }

{ OPTIONAL {pattern } }

{ { } OPTIONAL {pattern } }

pattern OPTIONAL {pattern } OPTIONAL { pattern }

{pattern OPTIONAL {pattern } } OPTIONAL { pattern }

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>PREFIX rdf:        <http://www.w3.org/1999/02/22-rdf-syntax-ns#>_:a  rdf:type        foaf:Person ._:a  foaf:name       "Alice" ._:a  foaf:mbox       <mailto:alice@example.com> ._:a  foaf:mbox       <mailto:alice@work.example> ._:b  rdf:type        foaf:Person ._:b  foaf:name       "Bob" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE  {    ?x foaf:name  ?name .    OPTIONAL { ?x  foaf:mbox  ?mbox }}

There is no value ofmbox in the solution where the name is"Bob".

This query finds the names of people in the data. If there is a triple with predicatembox and the same subject, a solution will contain the object of that triple as well. In this example, only a single triple pattern is given in the optional match part of the query but, in general, the optional part may be any graph pattern. The entire optional graph pattern must match for the optional graph pattern to affect the query solution.

Constraints can be given in an optional graph pattern. For example:

PREFIX dc:   <http://purl.org/dc/elements/1.1/>PREFIX :     <http://example.org/book/>PREFIX ns:   <http://example.org/ns#>:book1  dc:title  "SPARQL Tutorial" .:book1  ns:price  42 .:book2  dc:title  "The Semantic Web" .:book2  ns:price  23 .

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title ?priceWHERE   {     ?x dc:title ?title .    OPTIONAL { ?x ns:price ?price . FILTER (?price < 30) }}

No price appears for the book with title "SPARQL Tutorial" because the optional graph pattern did not lead to a solution involving the variable "price".

Graph patterns are defined recursively. A graph pattern may have zero or more optional graph patterns, and any part of a query pattern may have an optional part. In this example, there are two optional graph patterns.

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice" ._:a  foaf:homepage   <http://work.example.org/alice/> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       <mailto:bob@work.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mbox ?hpageWHERE  {    ?x foaf:name  ?name .    OPTIONAL { ?x foaf:mbox ?mbox } .    OPTIONAL { ?x foaf:homepage ?hpage }}

Filtering of query solutions is done within aFILTER expression usingNOT EXISTS andEXISTS. Note that the filter scope rulesapply to the whole group in which the filter appears.

PREFIX  :       <http://example/>PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIX  foaf:   <http://xmlns.com/foaf/0.1/>:alice  rdf:type   foaf:Person .:alice  foaf:name  "Alice" .:bob    rdf:type   foaf:Person .

PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX  foaf:   <http://xmlns.com/foaf/0.1/> SELECT ?personWHERE {    ?person rdf:type  foaf:Person .    FILTER NOT EXISTS { ?person foaf:name ?name }}

PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#> PREFIX  foaf:   <http://xmlns.com/foaf/0.1/> SELECT ?personWHERE {    ?person rdf:type  foaf:Person .    FILTER EXISTS { ?person foaf:name ?name }}

The other style of negation provided in SPARQL isMINUS which evaluates both its arguments, then calculates solutions in the left-hand side that are not compatible with the solutions on the right-hand side.

PREFIX :       <http://example/>PREFIX foaf:   <http://xmlns.com/foaf/0.1/>:alice  foaf:givenName "Alice" ;        foaf:familyName "Smith" .:bob    foaf:givenName "Bob" ;        foaf:familyName "Jones" .:carol  foaf:givenName "Carol" ;        foaf:familyName "Smith" .

PREFIX :       <http://example/>PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT DISTINCT ?sWHERE {    ?s ?p ?o .    MINUS {        ?s foaf:givenName "Bob" .    }}

NOT EXISTS andMINUS represent two ways of thinking about negation, one based on testing whether a pattern exists in the data, given the bindings already determined by the query pattern, and one based on removing matches based on the evaluation of two patterns. In some cases they can produce different answers.

PREFIX : <http://example/>:a :b :c .

SELECT * {     ?s ?p ?o    FILTER NOT EXISTS { ?x ?y ?z }}

SELECT * {     ?s ?p ?o     MINUS     { ?x ?y ?z }}

PREFIX : <http://example/>SELECT * {      ?s ?p ?o     FILTER NOT EXISTS { :a :b :c }}

PREFIX : <http://example/>SELECT * {     ?s ?p ?o     MINUS { :a :b :c }}

PREFIX : <http://example.com/>:a :p 1 .:a :q 1 .:a :q 2 .:b :p 3.0 .:b :q 4.0 .:b :q 5.0 .

PREFIX : <http://example.com/>SELECT * WHERE {    ?x :p ?n    FILTER NOT EXISTS {        ?x :q ?m .        FILTER(?n = ?m)    }}

PREFIX : <http://example/>SELECT * WHERE {    ?x :p ?n    MINUS {        ?x :q ?m .        FILTER(?n = ?m)    }}

In the description below,iri is eitheran IRI written in full or abbreviated by a prefixed name, or the keyworda.elt is a path element, which may itself be composed of path constructs.

The order of IRIs, and reverse IRIs, in a negated property set is not significant and they can occur in a mixed order.

The precedence of the syntax forms is, from highest to lowest:

• IRI, prefixed names
• Negated property sets
• Groups
• Unary operators*,? and+
• Unary ^ inverse links
• Binary operator/
• Binary operator|

Precedence is left-to-right within groups.

Alternatives: Match one or both possibilities

{ :book1 dc:title|rdfs:label ?displayString }

which could have written:

{    :book1 <http://purl.org/dc/elements/1.1/title> | <http://www.w3.org/2000/01/rdf-schema#label> ?displayString}

Sequence: Find the name of any people that Alice knows.

{    ?x foaf:mbox <mailto:alice@example> .    ?x foaf:knows/foaf:name ?name .}

Sequence: Find the names of people 2 "foaf:knows" links away.

{     ?x foaf:mbox <mailto:alice@example> .    ?x foaf:knows/foaf:knows/foaf:name ?name .}

This is the same as the SPARQL query:

SELECT ?x ?name {    ?x  foaf:mbox <mailto:alice@example> .    ?x  foaf:knows [ foaf:knows [ foaf:name ?name ]]. }

or, with explicit variables:

SELECT ?x ?name {    ?x  foaf:mbox <mailto:alice@example> .    ?x  foaf:knows ?a1 .    ?a1 foaf:knows ?a2 .    ?a2 foaf:name ?name .}

Filtering duplicates: Because someone Alice knows may well know Alice, the example above may include Alice herself. This could be avoided with:

{ ?x foaf:mbox <mailto:alice@example> .  ?x foaf:knows/foaf:knows ?y .  FILTER ( ?x != ?y )  ?y foaf:name ?name }

Inverse Property Paths: These two are the same query: the second is just reversing the property direction which swaps the roles of subject and object.

{ ?x foaf:mbox <mailto:alice@example> }

{ <mailto:alice@example> ^foaf:mbox ?x }

Inverse Path Sequence: Find all the people who know someone?x knows.

{  ?x foaf:knows/^foaf:knows ?y .    FILTER(?x != ?y)}

which is equivalent to (?gen1 is a system generated variable):

{  ?x foaf:knows ?gen1 .  ?y foaf:knows ?gen1 .    FILTER(?x != ?y)}

Arbitrary length match: Find the names of all the people that can be reached from Alice byfoaf:knows:

{  ?x foaf:mbox <mailto:alice@example> .  ?x foaf:knows+/foaf:name ?name .}

Alternatives in an arbitrary length path:

{ ?ancestor (ex:motherOf|ex:fatherOf)+ <#me> }

Arbitrary length path match: Some forms of limited inference are possible as well. For example, for RDFS, all types and supertypes of a resource:

{ <http://example/thing> rdf:type/rdfs:subClassOf* ?type }

All resources and all their inferred types:

{ ?x rdf:type/rdfs:subClassOf* ?type }

Subproperty:

{ ?x ?p ?v . ?p rdfs:subPropertyOf* :property }

Negated Property Paths: Find nodes connected but not by rdf:type (either way round):

{ ?x !(rdf:type|^rdf:type) ?y }

Elements in an RDF collection:

{ :list rdf:rest*/rdf:first ?element }

Note: This path expression does not guarantee the order of the results.

SPARQL property paths treat the RDF triples as a directed, possibly cyclic, graph with named edges. Evaluation of a property path expression can lead to duplicates because any variables introduced in the equivalent pattern are not part of the results and are not already used elsewhere. They are hidden by implicit projection of the results to just the variables given in the query.

For example, on the data:

PREFIX :       <http://example/>:order  :item :z1 .:order  :item :z2 .:z1 :name "Small" .:z1 :price 5 .:z2 :name "Large" .:z2 :price 5 .

Query:

PREFIX :   <http://example/>SELECT * {  ?s :item/:price ?x . }

Results:

whereas if the query were written out to include the intermediate variable (?_a), no rows in the results are duplicates:

PREFIX :   <http://example/>SELECT * {  ?s :item ?_a .   ?_a :price ?x .}

Results:

The equivalence to graphs patterns is particularly significant when query also involves an aggregation operation. The total cost of the order can be found with

PREFIX :   <http://example/>SELECT (sum(?x) AS ?total) {     :order :item/:price ?x}

Connectivity between the subject and object by a property path of arbitrary length can be found using the "zero or more" property path operator,*, and the "one or more" property path operator,+. There is also a "zero or one" connectivity property path operator,?.

Each of these operators uses the property path expression to try to find a connection between subject and object, using the path step a number of times, as restricted by the operator.

For example, finding all the the possible types of a resource, including supertypes of resources, can be achieved with:

PREFIX  rdfs:   <http://www.w3.org/2000/01/rdf-schema#> . PREFIX  rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#>SELECT ?x ?type{     ?x rdf:type/rdfs:subClassOf* ?type}

Similarly, finding all the people:x connects to via thefoaf:knows relationship,

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX :     <http://example/>SELECT ?person{     :x foaf:knows+ ?person}

Such connectivity matching does not introduce duplicates (it does not incorporate any count of the number of ways the connection can be made) even if the repeated path itself would otherwise result in duplicates.

The graph matched may include cycles. Connectivity matching is defined so that matching cycles does not lead to undefined or infinite results.

TheBIND form allows a value to be assigned to a variable from a basic graph pattern or property path expression. Use ofBIND ends the preceding basic graph pattern. The variable introduced by theBIND clause must not have been used in the group graph pattern up to the point of use inBIND.

Example:

PREFIX dc:   <http://purl.org/dc/elements/1.1/>PREFIX :     <http://example.org/book/>PREFIX ns:   <http://example.org/ns#>:book1  dc:title     "SPARQL Tutorial" .:book1  ns:price     42 .:book1  ns:discount  0.2 .:book2  dc:title     "The Semantic Web" .:book2  ns:price     23 .:book2  ns:discount  0.25 .

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title ?price{       ?x ns:price ?p .    ?x ns:discount ?discount    BIND (?p*(1-?discount) AS ?price)    FILTER(?price < 20)    ?x dc:title ?title . }

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title ?price{  { ?x ns:price ?p .     ?x ns:discount ?discount     BIND (?p*(1-?discount) AS ?price)    }    {?x dc:title ?title . }    FILTER(?price < 20)}

Data can be directly written in a graph pattern or added to a query usingVALUES.VALUES provides inline data as asolution sequence which are combined with the results of query evaluation by ajoin operation. It can be used by an application to provide specific requirements on query results and also by SPARQL query engine implementations that providefederated query through theSERVICE keyword to send a more constrained query to a remote query service.

VALUES (?x ?y) {    (:uri1 1)    (:uri2 UNDEF)}

VALUES ?z { "abc" "def" }

VALUES (?z) { ("abc") ("def") }

PREFIX dc:   <http://purl.org/dc/elements/1.1/>PREFIX :     <http://example.org/book/>PREFIX ns:   <http://example.org/ns#>:book1  dc:title  "SPARQL Tutorial" .:book1  ns:price  42 .:book2  dc:title  "The Semantic Web" .:book2  ns:price  23 .

PREFIX dc:   <http://purl.org/dc/elements/1.1/> PREFIX :     <http://example.org/book/> PREFIX ns:   <http://example.org/ns#> SELECT ?book ?title ?price{    VALUES ?book { :book1 :book3 }    ?book dc:title ?title ;          ns:price ?price .}

PREFIX dc:   <http://purl.org/dc/elements/1.1/> PREFIX :     <http://example.org/book/> PREFIX ns:   <http://example.org/ns#> SELECT ?book ?title ?price{    ?book dc:title ?title ;          ns:price ?price .    VALUES (?book ?title) {        (UNDEF "SPARQL Tutorial")        (:book2 UNDEF)    }}

PREFIX dc:   <http://purl.org/dc/elements/1.1/> PREFIX :     <http://example.org/book/> PREFIX ns:   <http://example.org/ns#> SELECT ?book ?title ?price {    ?book dc:title ?title ;          ns:price ?price .}VALUES (?book ?title) {    (UNDEF "SPARQL Tutorial")    (:book2 UNDEF)}

PREFIX : <http://books.example/>:org1 :affiliates :auth1, :auth2 .:auth1 :writesBook :book1, :book2 .:book1 :price 9 .:book2 :price 5 .:auth2 :writesBook :book3 .:book3 :price 7 .:org2 :affiliates :auth3 .:auth3 :writesBook :book4 .:book4 :price 7 .

PREFIX : <http://books.example/>SELECT (SUM(?lprice) AS ?totalPrice)WHERE {    ?org :affiliates ?auth .    ?auth :writesBook ?book .    ?book :price ?lprice .}GROUP BY ?orgHAVING (SUM(?lprice) > 10)

This example demonstrates two features of aggregates:GROUP BY, which groups query solutions according to one or more expressions (in this case?org), andHAVING, which is analogous to aFILTER expression, but operates over groups, rather than individual solutions.

The example is produced by grouping solutions according to theGROUP BY expression (i.e. all solutions where?org takes a particular value appear within the same group), and evaluating the Set FunctionSUM over that group. The groups are then filtered by theHAVING expression, which removes all groups whereSUM(?lprice) is not greater than 10.

In aggregate queries and sub-queries, variables that appear in the query pattern, but are not in theGROUP BY clause, can only be projected or used in select expressions if they are aggregated. TheSAMPLE aggregate may be used for this purpose. For details see the section onProjection Restrictions.

It should be noted thatas per functions, aggregate expressions are required to be aliased (again, similar to theBIND clause, using the keywordAS) in order to project them from queries or subqueries. In the example above this is done using the variable?totalPrice. It is an error for aggregates to project variables with a name already used in other aggregate projections, or in theWHERE clause.

In order to calculate aggregate values for a solution, the solution is first divided into one or more groups, and the aggregate value is calculated for each group.

If aggregates are used in the query level inSELECT,HAVING orORDER BY but theGROUP BY term is not used, then this is taken to be a single implicit group, to which all solutions belong.

WithinGROUP BY clauses the binding keyword,AS, may be used, such asGROUP BY (?x + ?y AS ?z). This is equivalent to{ ... BIND (?x + ?y AS ?z) } GROUP BY ?z.

For example, given a solution sequenceS,( {?x→2, ?y→3}, {?x→2, ?y→5}, {?x→6, ?y→7} ), we might wish to group the solutions according to the value of?x, and calculate the average of the values of?y for each group.

This could be written as:

SELECT (AVG(?y) AS ?avg)WHERE {    ?a :x ?x ;    :y ?y .}GROUP BY ?x

HAVING operates over grouped solution sets, in the same way thatFILTER operates over un-grouped ones.

HAVING expressions have the same evaluation rules as projections from grouped queries, as described in the following section.

An example of the use ofHAVING is given below.

PREFIX : <http://data.example/>SELECT (AVG(?size) AS ?asize)WHERE {    ?x :size ?size}GROUP BY ?xHAVING(AVG(?size) > 10)

This will return average sizes, grouped by the subject, but only where the mean size is greater than 10.

In a query level which uses aggregates, only expressions consisting of aggregates and constants may be projected, with one exception. WhenGROUP BY is given with one or more simple expressions consisting of just a variable, those variables may be projected from the level.

For example, the following query is legal as ?x is given as aGROUP BY term.

PREFIX : <http://example.com/data/#>SELECT ?x (MIN(?y) * 2 AS ?min)WHERE {    ?x :p ?y .    ?x :q ?z .} GROUP BY ?x (STR(?z))

Note that it would not be legal to projectSTR(?z) as this is not a simple variable expression. However, withGROUP BY (STR(?z) AS ?strZ) it would be possible to project?strZ.

Other expressions, not usingGROUP BY variables, or aggregates may have non-deterministic values projected from their groups using theSAMPLE aggregate.

This section shows an example query using aggregation, which demonstrates how errors are handled in results, in the presence of aggregates.

Data:

PREFIX : <http://example.com/data/#>:x :p 1, 2, 3, 4 .:y :p 1, _:b2, 3, 4 .:z :p 1.0, 2.0, 3.0, 4 .

Query:

PREFIX : <http://example.com/data/#>SELECT ?g (AVG(?p) AS ?avg) ((MIN(?p) + MAX(?p)) / 2 AS ?c)WHERE {    ?g :p ?p .}GROUP BY ?g

Result:

Note that the bindings for the :y group is not included in the results as the evaluation of Avg({1, _:b2, 3, 4}), and (_:b2 + 4) / 2 is an error, removing the bindings from the solution.

Data:

PREFIX : <http://people.example/>:alice :name "Alice", "Alice Foo", "A. Foo" .:alice :knows :bob, :carol .:bob :name "Bob", "Bob Bar", "B. Bar" .:carol :name "Carol", "Carol Baz", "C. Baz" .

PREFIX : <http://people.example/>PREFIX : <http://people.example/>SELECT ?y ?minNameWHERE {    :alice :knows ?y .    {      SELECT ?y (MIN(?name) AS ?minName)      WHERE {          ?y :name ?name .      } GROUP BY ?y    }}

Results:

This result is achieved by first evaluating the inner query:

SELECT ?y (MIN(?name) AS ?minName)WHERE {    ?y :name ?name .} GROUP BY ?y

This produces the following solution sequence:

Which is joined with the results of the outer query:

Thedefinition of RDF Dataset [RDF12-CONCEPTS] does not restrict the relationships of named and default graphs. Information can be repeated in different graphs; relationships between graphs can be exposed. Two useful arrangements are:

• to have information in the default graph that includes provenance information about the named graphs
• to include the information in the named graphs in the default graph as well.

PREFIX dc: <http://purl.org/dc/elements/1.1/><http://example.org/bob>    dc:publisher  "Bob" .<http://example.org/alice>  dc:publisher  "Alice" .GRAPH <http://example.org/bob> {    _:a foaf:name "Bob" .    _:a foaf:mbox <mailto:bob@oldcorp.example.org> .}GRAPH <http://example.org/alice> {    _:a foaf:name "Alice" .    _:a foaf:mbox <mailto:alice@work.example.org> .}

In this example, the default graph contains the names of the publishers of two named graphs. The triples in the named graphs are not visible in the default graph in this example.

Example 2:

RDF data can be combined by theRDF merge [RDF12-SEMANTICS] of graphs. One possible arrangement of graphs in an RDF Dataset is to have the default graph be the RDF merge of some or all of the information in the named graphs.

In this next example, the named graphs contain the same triples as before. The RDF dataset includes anRDF merge of the named graphs in the default graph, which keeps blank nodes distinct.

PREFIX foaf: <http://xmlns.com/foaf/0.1/>_:x foaf:name "Bob" ._:x foaf:mbox <mailto:bob@oldcorp.example.org> ._:y foaf:name "Alice" ._:y foaf:mbox <mailto:alice@work.example.org> .GRAPH <http://example.org/bob> {    _:a foaf:name "Bob" .    _:a foaf:mbox <mailto:bob@oldcorp.example.org> .}GRAPH <http://example.org/alice> {    _:a foaf:name "Alice" .    _:a foaf:mbox <mailto:alice@work.example> .}

A SPARQL query may specify the dataset to be used for matching by using theFROM clause and theFROM NAMED clause to describe the RDF dataset. If a query provides such a dataset description, then it is used in place of any dataset that the query service would use if no dataset description is provided in a query. The RDF dataset may also bespecified in a SPARQL protocol request, in which case the protocol description overrides any description in the query itself. A query service may refuse a query request if the dataset description is not acceptable to the service.

TheFROM andFROM NAMED keywords allow a query to specify an RDF dataset by reference; they indicate that the dataset should include graphs that are obtained from representations of the resources identified by the given IRIs (i.e. the absolute form of the given IRI references). The dataset resulting from a number ofFROM andFROM NAMED clauses is:

• a default graph consisting of the RDF merge of the graphs referred to in theFROM clauses, and
• a set of (IRI, graph) pairs, one from eachFROM NAMED clause.

If there is noFROM clause, but there is one or moreFROM NAMED clauses, then the dataset includes an empty graph for the default graph.

# Default graph (located at http://example.org/foaf/aliceFoaf)PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>_:a  foaf:name     "Alice" ._:a  foaf:mbox     <mailto:alice@work.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT  ?nameFROM    <http://example.org/foaf/aliceFoaf>WHERE   { ?x foaf:name ?name }

# Graph: http://example.org/bobPREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Bob" ._:a foaf:mbox <mailto:bob@oldcorp.example.org> .

# Graph: http://example.org/alicePREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Alice" ._:a foaf:mbox <mailto:alice@work.example> .

...FROM NAMED <http://example.org/alice>FROM NAMED <http://example.org/bob>...

#Default graph (located at http://example.org/dft.ttl)PREFIX dc: <http://purl.org/dc/elements/1.1/><http://example.org/bob>    dc:publisher  "Bob Hacker" .<http://example.org/alice>  dc:publisher  "Alice Hacker" .

#Named graph: http://example.org/bobPREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Bob" ._:a foaf:mbox <mailto:bob@oldcorp.example.org> .

#Named graph: http://example.org/alicePREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Alice" ._:a foaf:mbox <mailto:alice@work.example.org> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT ?who ?g ?mboxFROM <http://example.org/dft.ttl>FROM NAMED <http://example.org/alice>FROM NAMED <http://example.org/bob>WHERE{    ?g dc:publisher ?who .    GRAPH ?g { ?x foaf:mbox ?mbox }}

When querying a collection of graphs, theGRAPH keyword is used to match patterns against named graphs.GRAPH can provide an IRI to select one graph or use a variable which will range over the IRI of all the named graphs in the query's RDF dataset.

The use ofGRAPH changes the active graph for matching graph patterns within that part of the query. Outside the use ofGRAPH, matching is done using the default graph.

The following two graphs will be used in examples:

# Named graph: http://example.org/foaf/aliceFoafPREFIX  foaf:     <http://xmlns.com/foaf/0.1/>PREFIX  rdf:      <http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIX  rdfs:     <http://www.w3.org/2000/01/rdf-schema#>_:a  foaf:name     "Alice" ._:a  foaf:mbox     <mailto:alice@work.example> ._:a  foaf:knows    _:b ._:b  foaf:name     "Bob" ._:b  foaf:mbox     <mailto:bob@work.example> ._:b  foaf:nick     "Bobby" ._:b  rdfs:seeAlso  <http://example.org/foaf/bobFoaf> .<http://example.org/foaf/bobFoaf>rdf:type      foaf:PersonalProfileDocument .

# Named graph: http://example.org/foaf/bobFoafPREFIX  foaf:     <http://xmlns.com/foaf/0.1/>PREFIX  rdf:      <http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIX  rdfs:     <http://www.w3.org/2000/01/rdf-schema#>_:z  foaf:mbox     <mailto:bob@work.example> ._:z  rdfs:seeAlso  <http://example.org/foaf/bobFoaf> ._:z  foaf:nick     "Robert" .<http://example.org/foaf/bobFoaf>        rdf:type      foaf:PersonalProfileDocument .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?src ?bobNickFROM NAMED <http://example.org/foaf/aliceFoaf>FROM NAMED <http://example.org/foaf/bobFoaf>WHERE{    GRAPH ?src    { ?x foaf:mbox <mailto:bob@work.example> .      ?x foaf:nick ?bobNick    }}

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX data: <http://example.org/foaf/>SELECT ?nickFROM NAMED <http://example.org/foaf/aliceFoaf>FROM NAMED <http://example.org/foaf/bobFoaf>WHERE{    GRAPH data:bobFoaf {        ?x foaf:mbox <mailto:bob@work.example> .        ?x foaf:nick ?nick     }}

PREFIX  data:  <http://example.org/foaf/>PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>PREFIX  rdfs:  <http://www.w3.org/2000/01/rdf-schema#>SELECT ?mbox ?nick ?ppdFROM NAMED <http://example.org/foaf/aliceFoaf>FROM NAMED <http://example.org/foaf/bobFoaf>WHERE {    GRAPH data:aliceFoaf {        ?alice foaf:mbox <mailto:alice@work.example> ;               foaf:knows ?whom .        ?whom  foaf:mbox ?mbox ;               rdfs:seeAlso ?ppd .        ?ppd  a foaf:PersonalProfileDocument .    }    GRAPH ?ppd {        ?w foaf:mbox ?mbox ;           foaf:nick ?nick    }}

Any triple in Alice's FOAF file giving Bob'snick is not used to provide a nick for Bob because the pattern involving variablenick is restricted byppd to a particular Personal Profile Document.

#Default graphPREFIX dc: <http://purl.org/dc/elements/1.1/>PREFIX g:  <tag:example.org,2005-06-06:>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>g:graph1 dc:publisher "Bob" .g:graph1 dc:date "2004-12-06"^^xsd:date .g:graph2 dc:publisher "Bob" .g:graph2 dc:date "2005-01-10"^^xsd:date .

#Graph: locally allocated IRI: tag:example.org,2005-06-06:graph1PREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Alice" ._:a foaf:mbox <mailto:alice@work.example> ._:b foaf:name "Bob" ._:b foaf:mbox <mailto:bob@oldcorp.example.org> .

#Graph: locally allocated IRI: tag:example.org,2005-06-06:graph2PREFIX foaf: <http://xmlns.com/foaf/0.1/>_:a foaf:name "Alice" ._:a foaf:mbox <mailto:alice@work.example> ._:b foaf:name "Bob" ._:b foaf:mbox <mailto:bob@newcorp.example.org> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc:   <http://purl.org/dc/elements/1.1/>SELECT ?name ?mbox ?dateWHERE {   ?g dc:publisher ?name ;      dc:date ?date .   GRAPH ?g {        ?person foaf:name ?name ; foaf:mbox ?mbox   }}

TheORDER BY clause establishes the order of a solution sequence.

Following theORDER BY clause is a sequence of order comparators, composed of an expression and an optional order modifier (eitherASC() orDESC()). Each ordering comparator is either ascending (indicated by theASC() modifier or by no modifier) or descending (indicated by theDESC() modifier).

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE { ?x foaf:name ?name }ORDER BY ?name

PREFIX     :    <http://example.org/ns#>PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE { ?x foaf:name ?name ; :empId ?emp }ORDER BY DESC(?emp)

PREFIX     :    <http://example.org/ns#>PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE { ?x foaf:name ?name ; :empId ?emp }ORDER BY ?name DESC(?emp)

The"<" operator (see theOperator Mapping and17.3.1 Operator Extensibility) defines the relative order of pairs ofnumerics,xsd:strings,xsd:booleans andxsd:dateTimes. Pairs of IRIs are ordered by comparing them as literals with datatypexsd:string.

SPARQL also fixes an order between some kinds of RDF terms that would not otherwise be ordered:

1. (Lowest) no value assigned to the variable or expression in this solution.
2. Blank nodes
3. IRIs
4. RDF literals

SPARQL does not define a total ordering of all possible RDF terms. Here are a few examples of pairs of terms for which the relative order is undefined:

• "a" and "a"@en_gb (a literal with datatypexsd:string and a literal with a language tag)
• "a"@en_gb and "b"@en_gb (two literals with language tags)
• "a" and "1"^^xsd:integer (a literal with datatypexsd:string and a literal with a supported datatype)
• "1"^^my:integer and "2"^^my:integer (two unsupported datatypes)
• "1"^^xsd:integer and "2"^^my:integer (a supported datatype and an unsupported datatype)

This list of variable bindings is in ascending order:

The ascending order of two solutions with respect to an ordering comparator is established by substituting the solution bindings into the expressions and comparing them with the"<" operator. The descending order is the reverse of the ascending order.

The relative order of two solutions is the relative order of the two solutions with respect to the first ordering comparator in the sequence. For solutions where the substitutions of the solution bindings produce the same RDF term, the order is the relative order of the two solutions with respect to the next ordering comparator. The relative order of two solutions is undefined if no order expression evaluated for the two solutions produces distinct RDF terms.

Ordering a sequence of solutions always results in a sequence with the same number of solutions in it.

UsingORDER BY on a solution sequence for aCONSTRUCT orDESCRIBE query has no direct effect because onlySELECT returns a sequence of results. Used in combination withLIMIT andOFFSET,ORDER BY can be used to return results generated from a different slice of the solution sequence. AnASK query does not includeORDER BY,LIMIT orOFFSET.

The solution sequence can be transformed into one involving only a subset of the variables. For each solution in the sequence, a new solution is formed using a specified selection of the variables using the SELECT query form.

The following example shows a query to extract just the names of people described in an RDF graph using FOAF properties.

PREFIX foaf:        <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice" ._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       <mailto:bob@work.example> .

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE{ ?x foaf:name ?name }

A solution sequence with noDISTINCT orREDUCED query modifier will preserve duplicate solutions.

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>_:x    foaf:name   "Alice" ._:x    foaf:mbox   <mailto:alice@example.com> ._:y    foaf:name   "Alice" ._:y    foaf:mbox   <mailto:asmith@example.com> ._:z    foaf:name   "Alice" ._:z    foaf:mbox   <mailto:alice.smith@example.com> .

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?name WHERE { ?x foaf:name ?name }

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT DISTINCT ?name WHERE { ?x foaf:name ?name }

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT REDUCED ?name WHERE { ?x foaf:name ?name }

OFFSET causes the solutions generated to start after the specified number of solutions. AnOFFSET of zero has no effect.

UsingLIMIT andOFFSET to select different subsets of the query solutions will not be useful unless the order is made predictable by usingORDER BY.

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT  ?nameWHERE   { ?x foaf:name ?name }ORDER BY ?nameLIMIT   5OFFSET  10

TheLIMIT clause puts an upper bound on the number of solutions returned. If the number of actual solutions, afterOFFSET is applied, is greater than the limit, then at most the limit number of solutions will be returned.

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE { ?x foaf:name ?name }LIMIT 20

ALIMIT of 0 would cause no results to be returned. A limit may not be negative.

The SELECT form of results returns variables and their bindings directly. It combines the operations of projecting the required variables with introducing new variable bindings into a query solution.

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>_:a    foaf:name   "Alice" ._:a    foaf:knows  _:b ._:a    foaf:knows  _:c ._:b    foaf:name   "Bob" ._:c    foaf:name   "Clare" ._:c    foaf:nick   "CT" .

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>SELECT ?nameX ?nameY ?nickYWHERE{ ?x foaf:knows ?y ;  foaf:name ?nameX .  ?y foaf:name ?nameY .  OPTIONAL { ?y foaf:nick ?nickY }}

{    "head": {        "vars": [ "nameX" , "nameY" , "nickY" ]    } ,    "results": {        "bindings": [          {            "nameX": { "type": "literal" , "value": "Alice" } ,            "nameY": { "type": "literal" , "value": "Bob" }          } ,          {            "nameX": { "type": "literal" , "value": "Alice" } ,            "nameY": { "type": "literal" , "value": "Clare" } ,            "nickY": { "type": "literal" , "value": "CT" }          }        ]    }}

<?xml version="1.0"?><sparql xmlns="http://www.w3.org/2005/sparql-results#"><head><variable name="nameX"/><variable name="nameY"/><variable name="nickY"/></head><results><result><binding name="nameX"><literal>Alice</literal></binding><binding name="nameY"><literal>Bob</literal></binding></result><result><binding name="nameX"><literal>Alice</literal></binding><binding name="nameY"><literal>Clare</literal></binding><binding name="nickY"><literal>CT</literal></binding></result></results></sparql>

PREFIX dc:   <http://purl.org/dc/elements/1.1/>PREFIX :     <http://example.org/book/>PREFIX ns:   <http://example.org/ns#>:book1  dc:title  "SPARQL Tutorial" .:book1  ns:price  42 .:book1  ns:discount 0.2 .:book2  dc:title  "The Semantic Web" .:book2  ns:price  23 .:book2  ns:discount 0.25 .

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title (?p*(1-?discount) AS ?price){ ?x ns:price ?p .  ?x dc:title ?title .   ?x ns:discount ?discount }

PREFIX  dc:  <http://purl.org/dc/elements/1.1/>PREFIX  ns:  <http://example.org/ns#>SELECT  ?title (?p AS ?fullPrice) (?fullPrice*(1-?discount) AS ?customerPrice){ ?x ns:price ?p .  ?x dc:title ?title .   ?x ns:discount ?discount }

TheCONSTRUCT query form returns a single RDF graph specified by a graph template. The result is an RDF graph formed by taking each query solution in the solution sequence, substituting for the variables in the graph template, and combining the triples into a single RDF graph by set union.

If any such instantiation produces a triple containing an unbound variable or an illegal RDF construct, such as a literal in subject or predicate position, then that triple is not included in the output RDF graph. The graph template can contain triples with no variables (known as ground or explicit triples), and these also appear in the output RDF graph returned by the CONSTRUCT query form.

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>_:a    foaf:name   "Alice" ._:a    foaf:mbox   <mailto:alice@example.org> .

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>PREFIX vcard:   <http://www.w3.org/2001/vcard-rdf/3.0#>CONSTRUCT   { <http://example.org/person#Alice> vcard:FN ?name }WHERE       { ?x foaf:name ?name }

PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#><http://example.org/person#Alice> vcard:FN "Alice" .

PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>_:a    foaf:givenname   "Alice" ._:a    foaf:family_name "Hacker" ._:b    foaf:firstname   "Bob" ._:b    foaf:surname     "Hacker" .

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>PREFIX vcard:   <http://www.w3.org/2001/vcard-rdf/3.0#>CONSTRUCT {     ?x  vcard:N _:v .    _:v vcard:givenName ?gname .    _:v vcard:familyName ?fname} WHERE {    { ?x foaf:firstname ?gname } UNION  { ?x foaf:givenname   ?gname } .    { ?x foaf:surname   ?fname } UNION  { ?x foaf:family_name ?fname } .}

PREFIX vcard: <http://www.w3.org/2001/vcard-rdf/3.0#>_:a vcard:N         _:v1 ._:v1 vcard:givenName  "Alice" ._:v1 vcard:familyName "Hacker" ._:b vcard:N         _:v2 ._:v2 vcard:givenName  "Bob" ._:v2 vcard:familyName "Hacker" .

CONSTRUCT { ?s ?p ?o } WHERE { GRAPH <http://example.org/aGraph> { ?s ?p ?o } . }

PREFIX  dc: <http://purl.org/dc/elements/1.1/>PREFIX app: <http://example.org/ns#>PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>CONSTRUCT { ?s ?p ?o } WHERE{    GRAPH ?g { ?s ?p ?o } .    ?g dc:publisher <http://www.w3.org/> .    ?g dc:date ?date .    FILTER ( app:customDate(?date) > "2005-02-28T00:00:00Z"^^xsd:dateTime ) .}

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX site: <http://example.org/stats#>_:a foaf:name "Alice" ._:a site:hits 2349 ._:b foaf:name "Bob" ._:b site:hits 105 ._:c foaf:name "Eve" ._:c site:hits 181 .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX site: <http://example.org/stats#>CONSTRUCT { [] foaf:name ?name }WHERE{ [] foaf:name ?name ;  site:hits ?hits .}ORDER BY desc(?hits)LIMIT 2

PREFIX foaf: <http://xmlns.com/foaf/0.1/>_:x foaf:name "Alice" ._:y foaf:name "Eve" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>CONSTRUCT WHERE { ?x foaf:name ?name }

PREFIX foaf: <http://xmlns.com/foaf/0.1/>CONSTRUCT { ?x foaf:name ?name } WHERE{ ?x foaf:name ?name }

Applications can use theASK form to test whether or not a query pattern has a solution. No information is returned about the possible query solutions, just whether or not a solution exists.

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice" ._:a  foaf:homepage   <http://work.example.org/alice/> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       <mailto:bob@work.example> .

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>ASK  { ?x foaf:name  "Alice" }

true

<?xml version="1.0"?>                <sparql xmlns="http://www.w3.org/2005/sparql-results#">                <head></head>                <boolean>true</boolean>                </sparql>

PREFIX foaf:    <http://xmlns.com/foaf/0.1/>ASK  {   ?x foaf:name  "Alice" ;      foaf:mbox  <mailto:alice@work.example>}

false

TheDESCRIBE form returns a single result RDF graph containing RDF data about resources. This data is not prescribed by a SPARQL query, where the query client would need to know the structure of the RDF in the data source, but, instead, is determined by the SPARQL query processor. The query pattern is used to create a result set. TheDESCRIBE form takes each of the resources identified in a solution, together with any resources directly named by IRI, and assembles a single RDF graph by taking a "description" which can come from any information available including the target RDF Dataset. The description is determined by the query service. The syntaxDESCRIBE * is an abbreviation that describes all of the variables in a query.

DESCRIBE <http://example.org/>

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>DESCRIBE ?xWHERE    { ?x foaf:mbox <mailto:alice@org> }

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>DESCRIBE ?xWHERE    { ?x foaf:name "Alice" }

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>DESCRIBE ?x ?y <http://example.org/>WHERE    {?x foaf:knows ?y}

PREFIX ent:  <http://org.example.com/employees#>DESCRIBE ?x WHERE { ?x ent:employeeId "1234" }

PREFIX foaf:   <http://xmlns.com/foaf/0.1/>PREFIX vcard:  <http://www.w3.org/2001/vcard-rdf/3.0>PREFIX exOrg:  <http://org.example.com/employees#>PREFIX rdf:    <http://www.w3.org/1999/02/22-rdf-syntax-ns#>PREFIX owl:    <http://www.w3.org/2002/07/owl#>_:a     exOrg:employeeId    "1234" ;        foaf:mbox_sha1sum   "bee135d3af1e418104bc42904596fe148e90f033" ;        vcard:N          [ vcard:Family       "Smith" ;            vcard:Given        "John"  ] .foaf:mbox_sha1sum  rdf:type  owl:InverseFunctionalProperty .

SPARQL functions and operators operate on RDF terms and SPARQL variables. A subset of these functions and operators are taken from theXPath and XQuery Functions and Operators 3.1 [XPATH-FUNCTIONS-31] and have XML Schematyped value arguments and return types. RDFliterals passed as arguments to these functions and operators are mapped to XML Schema typed values with astring value of thelexical form and anatomic datatype corresponding to thedatatype IRI. The returned typed values are mapped back to RDFliterals the same way.

SPARQL has additional operators which operate on specific subsets of RDF terms. When referring to a type, the following terms denote aliteral with the correspondingW3C XML Schema Definition Language (XSD) 1.1 Part 2: Datatypes [XMLSCHEMA11-2]datatype IRI:

• xsd:integer
• xsd:decimal
• xsd:float
• xsd:double
• xsd:string
• xsd:boolean
• xsd:dateTime

The following terms identify additional types used in SPARQL value tests:

• numeric denotesliterals with datatypesxsd:integer,xsd:decimal,xsd:float, orxsd:double.
• RDF term denotes the typesIRI,literal,blank node, ortriple term.
• variable denotes a SPARQL variable.

The following types are derived fromnumeric types and are valid arguments to functions and operators takingnumeric arguments:

• xsd:nonPositiveInteger
• xsd:negativeInteger
• xsd:long
• xsd:int
• xsd:short
• xsd:byte
• xsd:nonNegativeInteger
• xsd:unsignedLong
• xsd:unsignedInt
• xsd:unsignedShort
• xsd:unsignedByte
• xsd:positiveInteger

SPARQL language extensions may treat additional types as being derived from XML schema datatypes.

SPARQL provides a subset of the functions and operators defined by XQueryOperator Mapping. The XQuery sectionExpression Processing describes the invocation of XPath functions. The following rules accommodate the differences in the data and execution models between XQuery and SPARQL:

• Unlike XPath/XQuery, SPARQL functions do not process node sequences. When interpreting the semantics of XPath functions, assume that each argument is a sequence of a single node.
• Functions invoked with an argument of the wrong type will produce atype error. Effective boolean value arguments (labeled "xsd:boolean (EBV)" in the operator mapping table below), are coerced toxsd:boolean using theEBV rules in section 17.2.2.
• Apart from thefunctional formsBOUND,COALESCE,IF,IN,NOT IN,logical-or (||),logical-and (&&),NOT EXISTS, andEXISTS, all functions operate on RDF Terms and will produce a type error if any arguments are unbound.
• Any expression other thanlogical-or (||) orlogical-and (&&) that encounters an error will produce that error.
• Alogical-or that encounters an error on only one branch will return TRUE if the other branch is TRUE and an error if the other branch is FALSE.
• Alogical-and that encounters an error on only one branch will return an error if the other branch is TRUE and FALSE if the other branch is FALSE.
• Alogical-or orlogical-and that encounters errors on both branches will produceeither of the errors.

The logical-and and logical-or truth table for true (T), false (F), and error (E) is as follows:

The SPARQL grammar identifies a set of operators (for instance,&&,*,isIRI) used to construct constraints. The following table associates each of these grammatical productions with the appropriate operands and an operator function defined by eitherXPath and XQuery Functions and Operators 3.1 [XPATH-FUNCTIONS-31] or the SPARQL operators specified insection 17.4. When selecting the operator definition for a given set of parameters, the definition with the most specific parameters applies. For instance, when evaluatingxsd:integer = xsd:signedInt, the definition for= with twonumeric parameters applies, rather than the one with twoRDF terms. The table is arranged so that the upper-most viable candidate is the most specific. Operators invoked without appropriate operands result in a type error.

SPARQL follows XPath's scheme for numeric type promotions and subtype substitution for arguments to numeric operators. TheXPath Operator Mapping rules fornumeric operands (xsd:integer,xsd:decimal,xsd:float,xsd:double, and types derived from anumeric type) apply to SPARQL operators as well (seeXML Path Language (XPath) 3.1 [XPATH-31] for definitions ofnumeric type promotions andsubtype substitution). Some of the operators are associated with nested function expressions, e.g.fn:not(op:numeric-equal(A, B)). Note that per the XPath definitions,fn:not andop:numeric-equal produce an error if their argument is an error.

The collation forfn:compare isdefined by XPath and identified byhttp://www.w3.org/2005/xpath-functions/collation/codepoint. This collation allows for string comparison based on code point values. Codepoint string equivalence can be tested withRDF term equivalence.

This section defines the operators and functions introduced by the SPARQL query language. The examples show the behavior of the operators as invoked by the appropriate grammatical constructs.

xsd:booleanBOUND (variablevar)

PREFIX foaf:        <http://xmlns.com/foaf/0.1/>PREFIX dc:          <http://purl.org/dc/elements/1.1/>PREFIX xsd:          <http://www.w3.org/2001/XMLSchema#>_:a  foaf:givenName  "Alice"._:b  foaf:givenName  "Bob" ._:b  dc:date         "2005-04-04T04:04:04Z"^^xsd:dateTime .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc:   <http://purl.org/dc/elements/1.1/>PREFIX xsd:   <http://www.w3.org/2001/XMLSchema#>SELECT ?givenNameWHERE {   ?x foaf:givenName  ?givenName .   OPTIONAL { ?x dc:date ?date } .   FILTER ( bound(?date) )}

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX dc:   <http://purl.org/dc/elements/1.1/>SELECT ?nameWHERE {     ?x foaf:givenName  ?name .    OPTIONAL { ?x dc:date ?date } .    FILTER (!bound(?date)) }

rdfTermIF (expression1,expression2,expression3)

rdfTermCOALESCE(expression, ....)

xsd:booleanNOT EXISTS {pattern }

xsd:boolean EXISTS {pattern }

xsd:booleanlogical-or (xsd:booleanleft,xsd:booleanright)

xsd:booleanlogical-and (xsd:booleanleft,xsd:booleanright)

boolean  rdfTermIN (expression,...)

(rdfTerm = value of expression1) || (rdfTerm = value of expression2) || ...

boolean  rdfTermNOT IN (expression,...)

(rdfTerm != value of expression1) && (rdfTerm != value of expression2) && ...

xsd:booleanRDFterm-equal (RDF termterm1,RDF termterm2)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice"._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Ms A."._:b  foaf:mbox       <mailto:alice@work.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name1 ?name2WHERE {    ?x foaf:name  ?name1 ;       foaf:mbox  ?mbox1 .    ?y foaf:name  ?name2 ;       foaf:mbox  ?mbox2 .    FILTER (?mbox1 = ?mbox2 && ?name1 != ?name2)}

PREFIX a:          <http://www.w3.org/2000/10/annotation-ns#>PREFIX dc:         <http://purl.org/dc/elements/1.1/>_:b   a:annotates   <http://www.w3.org/TR/rdf-sparql-query/> ._:b   dc:date       "2004-12-31T19:00:00-05:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> .

PREFIX a:      <http://www.w3.org/2000/10/annotation-ns#>PREFIX dc:     <http://purl.org/dc/elements/1.1/>PREFIX xsd:    <http://www.w3.org/2001/XMLSchema#>SELECT ?annotatesWHERE {    ?annot  a:annotates  ?annotates .    ?annot  dc:date      ?date .    FILTER ( ?date = xsd:dateTime("2005-01-01T00:00:00Z") ) }

xsd:booleansameTerm (RDF termterm1,RDF termterm2)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice"._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Ms A."._:b  foaf:mbox       <mailto:alice@work.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name1 ?name2WHERE {    ?x foaf:name  ?name1 ;       foaf:mbox  ?mbox1 .    ?y foaf:name  ?name2 ;       foaf:mbox  ?mbox2 .    FILTER (sameTerm(?mbox1, ?mbox2) && !sameTerm(?name1, ?name2))}

PREFIX :          <http://example.org/WMterms#>PREFIX t:         <http://example.org/types#>_:c1  :label        "Container 1" ._:c1  :weight       "100"^^t:kilos ._:c1  :displacement  "100"^^t:liters ._:c2  :label        "Container 2" ._:c2  :weight       "100"^^t:kilos ._:c2  :displacement  "85"^^t:liters ._:c3  :label        "Container 3" ._:c3  :weight       "85"^^t:kilos ._:c3  :displacement  "85"^^t:liters .

PREFIX  :      <http://example.org/WMterms#>PREFIX  t:     <http://example.org/types#>SELECT ?aLabel1 ?bLabelWHERE {    ?a  :label        ?aLabel .   ?a  :weight       ?aWeight .   ?a  :displacement ?aDisp .   ?b  :label        ?bLabel .   ?b  :weight       ?bWeight .   ?b  :displacement ?bDisp .   FILTER ( sameTerm(?aWeight, ?bWeight) && !sameTerm(?aDisp, ?bDisp)) }

xsd:booleanisIRI (RDF termterm)xsd:booleanisURI (RDF termterm)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice"._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       "bob@work.example" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE {    ?x foaf:name  ?name ;       foaf:mbox  ?mbox .    FILTER isIRI(?mbox) }

xsd:booleanisBLANK (RDF termterm)

PREFIX a:          <http://www.w3.org/2000/10/annotation-ns#>PREFIX dc:         <http://purl.org/dc/elements/1.1/>PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a   a:annotates   <http://www.w3.org/TR/rdf-sparql-query/> ._:a   dc:creator    "Alice B. Toeclips" ._:b   a:annotates   <http://www.w3.org/TR/rdf-sparql-query/> ._:b   dc:creator    _:c ._:c   foaf:given    "Bob"._:c   foaf:family   "Smith".

PREFIX a:      <http://www.w3.org/2000/10/annotation-ns#>PREFIX dc:     <http://purl.org/dc/elements/1.1/>PREFIX foaf:   <http://xmlns.com/foaf/0.1/>SELECT ?given ?familyWHERE {     ?annot  a:annotates  <http://www.w3.org/TR/rdf-sparql-query/> .    ?annot  dc:creator   ?c .    OPTIONAL { ?c  foaf:given   ?given ; foaf:family  ?family } .    FILTER isBLANK(?c)}

xsd:booleanisLITERAL (RDF termterm)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>                _:a  foaf:name       "Alice"._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       "bob@work.example" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE {    ?x foaf:name  ?name ;       foaf:mbox  ?mbox .    FILTER isLiteral(?mbox)}

xsd:booleanisNUMERIC (RDF termterm)

xsd:stringSTR (literalliteral)xsd:stringSTR (IRIrsrc)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice"._:a  foaf:mbox       <mailto:alice@work.example> ._:b  foaf:name       "Bob" ._:b  foaf:mbox       <mailto:bob@home.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE {    ?x foaf:name  ?name ;      foaf:mbox  ?mbox .    FILTER regex(str(?mbox), "@work\\.example$")}

xsd:stringLANG (literalltrl)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Robert"@en._:a  foaf:name       "Roberto"@es._:a  foaf:mbox       <mailto:bob@work.example> .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?name ?mboxWHERE {    ?x foaf:name  ?name ;       foaf:mbox  ?mbox .    FILTER ( lang(?name) = "es" )}

xsd:stringLANGDIR (literalltrl)

xsd:stringhasLANG (RDF termterm)

xsd:stringhasLANGDIR (RDF termterm)

iriDATATYPE (literalliteral)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>PREFIX eg:         <http://biometrics.example/ns#>PREFIX xsd:        <http://www.w3.org/2001/XMLSchema#>_:a  foaf:name       "Alice"._:a  eg:shoeSize     "9.5"^^xsd:float ._:b  foaf:name       "Bob"._:b  eg:shoeSize     "42"^^xsd:integer .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX xsd:  <http://www.w3.org/2001/XMLSchema#>PREFIX eg:   <http://biometrics.example/ns#>SELECT ?name ?shoeSizeWHERE {     ?x foaf:name  ?name ;       eg:shoeSize  ?shoeSize .    FILTER ( datatype(?shoeSize) = xsd:integer )}

iriIRI(xsd:string)iriIRI(iri)iriURI(xsd:string)iriURI(iri)

blank nodeBNODE()

blank nodeBNODE(xsd:string)

literalSTRDT(xsd:string lexicalForm,IRI datatypeIRI)

literalSTRLANG(xsd:string lexicalForm,xsd:string langTag)

literalSTRLANGDIR(xsd:string lexicalForm,xsd:string langTag,xsd:string baseDirection)

iriUUID()

xsd:stringSTRUUID()

xsd:integerSTRLEN(string literal str)

string literalSUBSTR(string literal source,xsd:integer startingLoc)string literalSUBSTR(string literal source,xsd:integer startingLoc,xsd:integer length)

string literalUCASE(string literal str)

string literalLCASE(string literal str)

xsd:booleanSTRSTARTS(string literal arg1,string literal arg2)

xsd:booleanSTRENDS(string literal arg1,string literal arg2)

xsd:booleanCONTAINS(string literal arg1,string literal arg2)

literalSTRBEFORE(string literal arg1,string literal arg2)

literalSTRAFTER(string literal arg1,string literal arg2)

string literalCONCAT(string literal, ...,string literal)

xsd:booleanlangMatches (xsd:stringlanguage-tag,xsd:stringlanguage-range)

PREFIX dc:       <http://purl.org/dc/elements/1.1/>_:a  dc:title         "That Seventies Show"@en ._:a  dc:title         "Cette Série des Années Soixante-dix"@fr ._:a  dc:title         "Cette Série des Années Septante"@fr-BE ._:b  dc:title         "Il Buono, il Bruto, il Cattivo" .

PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT ?titleWHERE {    ?x dc:title  "That Seventies Show"@en ;       dc:title  ?title .    FILTER langMatches( lang(?title), "FR" )}

PREFIX dc: <http://purl.org/dc/elements/1.1/>SELECT ?titleWHERE {    ?x dc:title  ?title .    FILTER langMatches( lang(?title), "*" )}

xsd:booleanREGEX (string literaltext,xsd:stringpattern)xsd:booleanREGEX (string literaltext,xsd:stringpattern,xsd:stringflags)

PREFIX foaf:       <http://xmlns.com/foaf/0.1/>_:a  foaf:name       "Alice"._:b  foaf:name       "Bob" .

PREFIX foaf: <http://xmlns.com/foaf/0.1/>SELECT ?nameWHERE {     ?x foaf:name  ?name    FILTER regex(?name, "^ali", "i")}

string literalREPLACE (string literal arg,xsd:string pattern,xsd:string replacement )string literalREPLACE (string literal arg,xsd:string pattern,xsd:string replacement,xsd:string flags)

xsd:stringENCODE_FOR_URI(string literal ltrl)

numericABS (numericterm)

numericROUND (numericterm)

numericCEIL (numericterm)

numericFLOOR (numericterm)

xsd:doubleRAND ( )

xsd:dateTimeNOW ()

xsd:integerYEAR (xsd:dateTimearg)

xsd:integerMONTH (xsd:dateTimearg)

xsd:integerDAY (xsd:dateTimearg)

xsd:integerHOURS (xsd:dateTimearg)

xsd:integerMINUTES (xsd:dateTimearg)

xsd:decimalSECONDS (xsd:dateTimearg)

xsd:dayTimeDurationTIMEZONE (xsd:dateTimearg)

xsd:stringTZ (xsd:dateTimearg)

triple termTRIPLE (RDF termsubj,RDF termpred,RDF termobj)

<<( subj pred obj)>>

PREFIX : <http://example/>PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>SELECT ?s ?date {    ?s ?p ?o .    BIND( <<( ?s ?p ?o )>> AS ?tt )    :myreifier rdf:reifies ?tt .    :myreifier :tripleAdded ?date .}

PREFIX : <http://example/>PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>SELECT ?s ?date {    ?s ?p ?o .    BIND( TRIPLE(?s, ?p, ?o) AS ?tt )    :myreifier rdf:reifies ?tt .    :myreifier :tripleAdded ?date .}

RDF termSUBJECT (triple termtriple-term)

RDF termPREDICATE (triple termtriple-term)

RDF termOBJECT (triple termtriple-term)

xsd:booleanisTRIPLE (RDF termterm)

xsd:stringMD5 (xsd:stringarg)

xsd:stringSHA1 (xsd:stringarg)

xsd:stringSHA256 (xsd:stringarg)

xsd:stringSHA384 (xsd:stringarg)

xsd:stringSHA512 (xsd:stringarg)

SPARQL imports a subset of the XPath constructor functions defined inXPath and XQuery Functions and Operators 3.1 [XPATH-FUNCTIONS-31] in section19.1 Casting from primitive types to primitive types. SPARQL constructors include all of the XPath constructors for theSPARQL operand datatypes plus theadditional datatypes imposed by the RDF data model. Casting in SPARQL is performed by calling a constructor function for the target type on an operand of the source type.

XPath defines only the casts from one XML Schema datatype to another. The remaining cast is defined as follows:

• Casting anIRI to anxsd:string produces aliteral with a lexical value of the codepoints comprising the IRI, and a datatype ofxsd:string.

The table below summarizes the casting operations that are always allowed (Y), never allowed (N) and dependent on the lexical value (M). For example, a casting operation from anxsd:string (the first row) to anxsd:float (the second column) is dependent on the lexical value (M).

bool =xsd:boolean
dbl =xsd:double
flt =xsd:float
dec =xsd:decimal
int =xsd:integer
dT =xsd:dateTime
str =xsd:string
IRI =IRI

It should be noted that any function or operator that is specified to return an error under some conditions is a valid extension point. That is, an implementation may return a non-error value in these error cases, and still be conformant with this recommendation.

APrimaryExpression grammar rule can be a call to an extension function named by an IRI. An extension function takes some number of RDF terms as arguments and returns an RDF term. The semantics of these functions are identified by the IRI that identifies the function.

SPARQL queries using extension functions are likely to have limited interoperability.

As an example, consider a function calledfunc:even:

xsd:booleanfunc:even (numericvalue)

PREFIX foaf: <http://xmlns.com/foaf/0.1/>PREFIX func: <http://example.org/functions#>SELECT ?name ?idWHERE {     ?x foaf:name  ?name ;       func:empId   ?id .    FILTER (func:even(?id))}

For a second example, consider a functionaGeo:distance that calculates the distance between two points, which is used here to find the places near Grenoble:

xsd:doubleaGeo:distance (numericx1,numericy1,numericx2,numericy2)

PREFIX aGeo: <http://example.org/geo#>SELECT ?neighborWHERE {    ?a aGeo:placeName "Grenoble" .    ?a aGeo:locationX ?axLoc .    ?a aGeo:locationY ?ayLoc .    ?b aGeo:placeName ?neighbor .    ?b aGeo:locationX ?bxLoc .    ?b aGeo:locationY ?byLoc .    FILTER ( aGeo:distance(?axLoc, ?ayLoc, ?bxLoc, ?byLoc) < 10 ) .}

An extension function might be used to test some application datatype not supported by the core SPARQL specification, it might be a transformation between datatype formats, for example into an XSD dateTime RDF term from another date format.

This section defines the process of converting graph patterns and solution modifiers in a SPARQL query string into a SPARQL algebra expression. The process described converts one level of query nesting, as formed by subqueries using the nestedSELECT syntax and is applied recursively on subqueries. Each level consists of graph pattern matching and filtering, followed by the application of solution modifiers.

The SPARQL query string is parsed and the abbreviations for IRIs and triple patterns given insection 4 are applied. At this point the abstract syntax tree is composed of:

The result of converting such an abstract syntax tree is a SPARQL query that uses the following symbols in the SPARQL algebra:

Slice is the combination of OFFSET and LIMIT.

ToList is used where conversion from the results of graph pattern matching to sequences occurs.

ToMultiSet is used where conversion from a solution sequence to a multiset occurs.

OPTIONAL { { ...FILTER ( ... ?x ... ) } }..

Let FS := empty setFor each form FILTER(expr) in the group graph pattern    In expr, replace NOT EXISTS{P} with fn:not(exists(translate(P)))     In expr, replace EXISTS{P} with exists(translate(P))    FS := FS ∪ {expr}    End

Let A := undefined          For each element G in the GroupOrUnionGraphPattern    If A is undefined        A := Translate(G)    Else        A := Union(A, Translate(G))    EndThe result is A

If the form is GRAPH IRI GroupGraphPattern    The result is Graph(IRI, Translate(GroupGraphPattern))

If the form is GRAPH Var GroupGraphPattern    The result is Graph(Var, Translate(GroupGraphPattern))

Let FS := the empty setLet G := the empty pattern, a basic graph pattern which is the empty set.For each element E in the sequence of elements in the GroupGraphPattern    If E is of the form OPTIONAL{P}         Let A := Translate(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, Translate(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 := Translate(E)        G := Join(G, A)        End   End   The result is G.

The result is a multiset of solution mappings 'data'.

The result is ToMultiset(Translate(SubSelect))

If FS is not empty    Let G := output of preceding step    Let X := Conjunction of expressions in FS    G := Filter(X, G)End

Replace join(Z, A) by AReplace join(A, Z) by A

Let A := the empty sequenceLet Q := the query level being evaluatedLet P := the algebra translation of the GroupGraphPattern of the query levelLet E := [], a list of pairs of the form (variable, expression)If Q contains GROUP BY exprlist   Let Grp := Group(exprlist, ToList(P))Else If Q contains an aggregate in SELECT, HAVING, ORDER BY   Let Grp := Group((1), ToList(P))Else   skip the rest of the aggregate step   EndGlobal i := 1   # Initially 1 for each query processedFor each (X AS Var) in SELECT, each HAVING(X), and each ORDER BY X in Q  For each unaggregated variable V in X      Replace V with Sample(V)      End  For each aggregate R(args ; scalarvals) now in X      # note: scalarvals may be omitted; if so, it's equivalent to the empty function      Ai := Aggregation(args, R, scalarvals, Grp)      Replace R(...) with aggi in Q      i := i + 1      End  EndFor each variable V appearing outside of an aggregate   Ai := Aggregation(V, Sample, {}, Grp)   E := E append (V, aggi)   i := i + 1   EndA := Ai, ..., Ai-1P := AggregateJoin(A)

Let Q := the query level being evaluatedLet P := the algebra translation of the query level so farFor each HAVING(E) in Q    P := Filter(E, P)    End

Let P := the algebra translation of the query level so farP := Join(P, ToMultiSet(data))  where data is a solution sequence derived from the VALUES clause

SELECT selItem ... { pattern }SELECT * { pattern }

Let X := algebra from earlier stepsLet VS := list of all variables visible in the pattern,           so restricted by sub-SELECT projected variables and GROUP BY variables.           Not visible: only in filter, exists/not exists, masked by a subselect,                         non-projected GROUP variables, only in the right hand side of MINUSLet PV := {}, a set of variable namesNote, E is a list of pairs of the form (variable, expression), defined in section 18.2.4.  If "SELECT *"    PV := VSIf  "SELECT selItem ..."    For each selItem        If selItem is a variable            PV := PV ∪ { variable }        End        If selItem is (expr AS variable)            variable must not appear in VS nor in PV; if it does then generate a syntax error and stop            PV := PV ∪ { variable }            E := E append (variable, expr)         End    EndFor each pair (var, expr) in E    X := Extend(X, var, expr)    End  Result is X  The set PV is used later for projection.

When matching graph patterns, the possible solutions form amultiset, also known as abag. A multiset is an unordered collection of elements in which each element may appear more than once. It is described by a set of elements and a function giving the multiplicity of each of these elements (i.e., the number of times the element is contained in the multiset).

Writeμ for solution mappings.

Writeμ₀ for the mapping such thatdom(μ₀) is the empty set.

WriteΩ₀ for the multiset consisting of exactly the empty mappingμ₀, with multiplicity 1. This is the join identity.

Writeμ(x) for the solution mapping variablex to RDF termt : { (x,t) }.

WriteΩ(x) for the multiset consisting of exactlyμ(?x->t), that is,{ { (x, t) } } with multiplicity 1.

Here, μ₁(v) = μ₂(v) means that μ₁(v) and μ₂(v) are the same RDF term.

If μ₁ and μ₂ are compatible then μ₁ ∪ μ₂ is also a mapping. Write merge(μ₁, μ₂) for μ₁ ∪ μ₂

This section defines the evaluation ofproperty path patterns. A property path pattern is a subject endpoint (an RDF term or a variable), a property path express and an object endpoint. Thetranslation of property path expressions converts some forms to other SPARQL expressions, such as converting property paths of length one to triple patterns, which in turn are combined into basic graph patterns. This leaves property path operators ZeroOrOnePath, ZeroOrMorePath, OneOrMorePath and NegatedPropertySets and also path expressions contained within these operators.

All remaining property path expressions are present in the algebra in the formPath(X, path, Y) for endpoints X and Y. For example: syntax(:p/:q)* is a ZeroOrMorePath expression involving a sequence property path becoming the algebra expessionZeroOrMorePath(seq(link(:p), link(:q))).

eval(Path(X, PP,Y))

Var(x1, x2, ..., xn) = { xi | i in 1...n and xi is a variable}

All evaluation is carried out by matching theactive graph at that point in the overall query evaluation. We omit explicitly including the active graph in each definition for clarity.

eval(Path(X,link(iri), Y)) = evaluationof basic graph pattern {X iri Y}

If both X and Y are variables, this is the same as:

eval(Path(X:var,link(iri),Y:var)) = { (X, xn) (Y, yn) | xn and yn areRDF terms andtriple (xn iri yn) isin the active graph }

If X is a variable and Y an RDF term:

eval(Path(X:var,link(iri),Y:term)) = { (X, xn) | xn is anRDF term andtriple (xn iri Y) isin the active graph}

If X is an RDF term and Y is a variable:

eval(Path(X:term,link(iri),Y:var)) = { (Y, yn) | yn is anRDF term andtriple (X iri yn) isin the active graph}

If both X and Y are RDF terms:

eval(Path(X:term,link(iri),Y:term))     = { μ0 }iftriple (X iri Y) isin the active graph    = { { } } = Ω0eval(Path(X:term,link(iri),Y:term)) = { }iftriple (X iri Y) is notin the active graph

Informally, evaluating a Predicate Property Path is the same as executing a subquerySELECT * {X P Y } at that point in the query evaluation.

eval(Path(X,inv(P), Y)) =eval(Path(Y, P, X))

A =Join(eval(Path(X, P, V)),eval(Path(V, Q, Y)) )

eval(Path(X,seq(P,Q), Y)) =Project(A,Var(X,Y))

Informally, this is the same as:

SELECT * {XP _:a . _:a Q Y }

using the fact that a blank node_:a acts like a variable (under simple entailment) except it does not appear in the results fromSELECT *.

eval(Path(X,alt(P,Q), Y)) =Union(eval(Path(X, P, Y)),eval(Path(X, Q, Y)))

Informally, this is the same as:

SELECT * { {XPY } UNION {XQY } }

eval(Path(X:term,ZeroOrOnePath(P),Y:var)) =     { (Y, yn) | yn = X or {(Y, yn)}ineval(Path(X,P,Y)) }

eval(Path(X:var,ZeroOrOnePath(P),Y:term)) =    { (X, xn) | xn = Y or {(X, xn)}ineval(Path(X,P,Y)) }

eval(Path(X:term,ZeroOrOnePath(P),Y:term)) =     { {} }if X = Y oreval(Path(X,P,Y)) is not empty    { } othewise

eval(Path(X:var,ZeroOrOnePath(P),Y:var)) =     { (X, xn) (Y, yn) |either (yninnodes(G) and xn = yn) or {(X,xn), (Y,yn)}ineval(Path(X,P,Y)) }

We define an auxillary function, ALP, used in the definitions of ZeroOrMorePath and OneOrMorePath. Note that the algorithm given here serves to specify the feature. An implementation is free to implement evaluation by any method that produces the same results for the query overall. The ZeroOrMorePath and OneOrMorePath forms return matches based on distinct nodes connected by the path.

The matching algorithm is based on following all paths, and detecting when a graph node (subject or object), has been already visited on the path.

Informally, this algorithm attempts to extend the multiset of results by one application ofpath at each step, noting which nodes it has visited for this particular path. If a node has been visited for the path under consideration, it is not a candidate for another step.

Let eval(x:term, path) be the evaluation of'path', starting at RDF term x,  and returning a multiset of RDF terms reached  by repeated matches of path.ALP(x:term, path) =       Let V = empty setALP(x:term, path, V)      return is V  # V is the set of nodes visitedALP(x:term, path, V:set of RDF terms) =      if ( x in V ) return       add x to V      X =eval(x,path)       For n:term in XALP(n, path, V)          End

eval(Path(X:term,ZeroOrMorePath(path),vy:var)) =    { { (vy, n) } | ninALP(X, path) }eval(Path(vx:var,ZeroOrMorePath(path),vy:var)) =    { { (vx, t), (vy, n) } |  tinnodes(G), (vy, n)ineval(Path(t,ZeroOrMorePath(path), vy)) }eval(Path(vx:var,ZeroOrMorePath(path),y:term)) =eval(Path(y:term,ZeroOrMorePath(inv(path)),vx:var))eval(Path(x:term,ZeroOrMorePath(path),y:term)) =     { { } }if { (vy:var,y) }ineval(Path(x,ZeroOrMorePath(path) vy)    { } otherwise

# For OneOrMorePath, we take one step of the path then start# recording nodes for results.eval(Path(x:term, OneOrMorePath(path), vy:var)) =    Let X = eval(x, path)    Let V = the empty multiset    For n in X        ALP(n, path, V)    End    result is Veval(Path(vx:var, OneOrMorePath(path), vy:var)) =     { { (vx, t), (vy, n) } |  t in nodes(G), (vy, n) in eval(Path(t, OneOrMorePath(path), vy)) }eval(Path(vx:var, OneOrMorePath(path), y:term)) =    eval(Path(y:term, OneOrMorePath(inv(path)), vx))eval(Path(x:term, OneOrMorePath(path), y:term)) =    { { } } if { (vy:var, y) } in eval(Path(x, OneOrMorePath(path), vy))    { } otherwise

Write μ' as the extension of a solution mapping:μ'(μ,x) = μ(x)   if x is a variableμ'(μ,t) = t      if t is a RDF term

Let x and y be variables or RDF terms, and S a set of IRIs:   eval(Path(x, NPS(S), y)) = { μ | ∃ triple(μ'(μ,x), p, μ'(μ,y)) in G, such that the IRI of p ∉ S }

For each remaining symbol in a SPARQL abstract query, we define an operator for evaluation. The SPARQL algebra operators of the same name are used to evaluate SPARQL abstract query nodes as described in the section "Evaluation Semantics". Evaluation of basic graph patterns and property path patterns has been described above.

It is possible that a solution mapping μ in a Join can arise in different solution mappings, μ₁ and μ₂ in the multisets being joined. The multiplicity of  μ is the sum of the multiplicities from all possibilities.

The evaluation of expr(merge(μ, μ')) does not have an effective boolean value of true if it evaluates to false or if it raises an error.