Within the object position of a triple pattern, + we can use a triple term + or another triple pattern. +
+Such a triple pattern or nested triple pattern
+ is represented as a TripleTerm with
+ TripleTermSubject,
+ Verb, and
+ TripleTermObject, all
+ preceded by <<(, and
+ followed by )>>.
+ Note that triple terms and triple patterns
+ can be nested.
+
The example below shows how a triple pattern + can be used in the object position of another triple pattern.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+
+ SELECT ?person ?authority {
+ ?person :familyName "Smith" .
+ _:anno rdf:reifies <<( ?person :jobTitle "Designer" )>> .
+ _:anno :accordingTo ?authority .
+ }
+
+ Triple terms are mostly used
+ as the object of a triple
+ with a predicate of `rdf:reifies`.
+ Such a triple is called a reifying triple.
+ SPARQL also provides a shorthand notation for writing reifying triples
+ using the ReifiedTriple grammar production.
A ReifiedTriple
+ provides syntactic sugar to represent a reifying triple,
+ which defines a specific relationship between an
+ identifier (reifier)
+ and a triple term.
+ The identifier becomes a way to indirectly refer
+ to the triple term, which
+ may or may not be asserted within the query.
+
Reification using triple terms is a concept distinct from the + Reification vocabulary originally + defined in RDF Semantics. + While both terms describe a representation of an RDF triple using components, + RDF 1.2 and SPARQL 1.2 uses the term to identify a triple term + using the `rdf:reifies` predicate. +
+A reifying triple is represented using the
+ ReifiedTriple production
+ starting with <<,
+ followed by a ReifiedTripleSubject,
+ a Verb, and
+ a ReifiedTripleObject,
+ followed by an optional Reifier,
+ and ending with >>.
+ This Reifier is composed of a ~
+ followed by an optional rVarOrReifierId production.
+ This rVarOrReifierId is composed of
+ a variable, an IRI, or a blank node;
+ for example, `<< :subject :predicate :object ~ :IRIREF >>`.
+ If no reifier is present,
+ or the ~
+ is not immediately followed by variable,
+ an IRI, or a blank node —
+ as in `<< :subject :predicate :object >>`,
+ or `<< :subject :predicate :object ~ >>` —
+ a fresh RDF blank node is allocated.
+
ReifiedTriple's may be nested,
+ like
+
`<< ?subject1 :predicate1 << :subject2 :predicate2 :object2 >> ~ :IRIREF1 >>`
+ or
`<< :subject4 :predicate4 << :subject3 :predicate3 ?object3 ~ :IRIREF3 >> >>`.
+
The example below shows a reifying triple with an implicit reifier.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+
+ SELECT ?person ?authority {
+ ?person :familyName "Smith" .
+ << ?person :jobTitle "Designer" >> :accordingTo ?authority .
+ }
+
+ The example below shows a reifying triple with an explicit reifier.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+
+ SELECT ?person ?authority ?id {
+ ?person :familyName "Smith" .
+ << ?person :jobTitle "Designer" ~ ?id >> :accordingTo ?authority .
+ }
+
+ The syntactic sugar of the example above expands to the following query:
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
+
+ SELECT ?person ?authority ?id {
+ ?person :familyName "Smith" .
+ ?id rdf:reifies <<( ?person :jobTitle "Designer" )>> .
+ ?id :accordingTo ?authority .
+ }
+
+ Note the subtle difference in syntax between the syntactic sugar of
+ the ReifiedTriple (i.e., `<< ... >>`)
+ and the regular TripleTerm (i.e., `<<( ... )>>`).
SPARQL also defines an annotation syntax + that both reifies and asserts a triple pattern, + which provides a convenient shortcut. + An annotation can be used to simultaneously assert a triple pattern, + via an explicit or implicit identifier, + and have that triple pattern be the + subject or + object of further triple patterns. + If explicitly identified, the same reifier can then be used as the + subject or + object of additional + triple patterns and/or triple terms. +
+Like a ReifiedTriple,
+ the annotation syntax uses a reifier — written as either a
+ variable, an IRI, or a blank node,
+ preceded by a tilde (~) —
+ to identify the
+ triple term being reified.
+ However, while the
+ ReifiedTriple syntax
+ may contain at most one reifier, the annotation syntax may contain
+ any number of reifiers. Each reifier causes a corresponding
+ reifying triple to be produced.
+
A reifier can be followed by an annotation block.
+ If a reifier is not followed by an annotation block, it is treated
+ analogously to a
+ ReifiedTriple
+ without additional annotations.
+ If an annotation block is not immediately preceded by a reifier,
+ a fresh RDF blank node is allocated to serve as the reifier of the
+ triple term.
+
The annotation syntax is a syntactic shortcut in SPARQL. + The RDF Abstract Syntax [[RDF11-CONCEPTS]] does not + distinguish how the triples were written.
+The example below shows an annotated triple pattern with an explicit reifier.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority {
+ ?person :name "Alice" ~ :t {| :statedBy ?authority ; :recorded "2021-07-07"^^xsd:date |} .
+ }
+
+ The syntactic sugar of the annotation syntax in the example above expands to the following query:
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority {
+ ?person :name "Alice" .
+ << ?person :name "Alice" ~ :t >> :statedBy ?authority ;
+ :recorded "2021-07-07"^^xsd:date .
+ }
+
+ If we fully expand this query to use TripleTerm's instead of reifiers,
+ the query is expanded to the following:
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority {
+ ?person :name "Alice" .
+ :t rdf:reifies <<( ?person :name "Alice" )>> .
+ :t :statedBy ?authority .
+ :t :recorded "2021-07-07"^^xsd:date .
+ }
+
+ The example below shows an annotated triple pattern with an implicit reifier, for which a fresh blank node is allocated.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority {
+ ?person :name "Alice" ~ :t {| :statedBy ?authority ; :recorded "2021-07-07"^^xsd:date |} .
+ }
+
+ An Annotation
+ may include any number of annotation blocks. If such blocks are not
+ immediately preceded by explicit reifiers, each block is associated
+ with a fresh blank node allocated as its reifier, as seen in the example below.
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority1 ?authority2 {
+ ?person :name "Alice"
+ {| :statedBy ?authority1 ; :recorded "2021-02-01"^^xsd:date |}
+ {| :statedBy ?authority2 ; :recorded "2021-07-07"^^xsd:date |} .
+ }
+
+ The query above will be fully expanded to the query below, where _:b0 and _:b1 stand for fresh RDF blank nodes.
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person ?authority1 ?authority2 {
+ ?person :name "Alice" .
+ _:b0 rdf:reifies <<( ?person :name "Alice" )>> .
+ _:b0 :statedBy ?authority1 .
+ _:b0 :recorded "2021-02-01"^^xsd:date .
+ _:b1 rdf:reifies <<( ?person :name "Alice" )>> .
+ _:b1 :statedBy ?authority2 .
+ _:b1 :recorded "2021-07-07"^^xsd:date .
+ }
+
+ The annotation syntax may also contain multiple explicit + reifiers without annotation blocks, as shown in the example below. Each such reifier + causes a corresponding reifying triple to be produced.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person {
+ ?person :name "Alice" ~ :stmt1 ~ stmt2 .
+ }
+
+ The query above will be fully expanded to the query below.
+
+ VERSION "1.2"
+ PREFIX : <http://example/>
+ PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
+
+ SELECT ?person {
+ ?person :name "Alice" .
+ :stmt1 rdf:reifies <<( ?person :name "Alice" )>> .
+ :stmt2 rdf:reifies <<( ?person :name "Alice" )>> .
+ }
+
+ To cope with the language evolution of SPARQL, @@ -13034,7 +13295,9 @@