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Add SPARQL syntax sections on triple terms, reifiers, and annotations #400

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Add SPARQL syntax sections on triple terms, reifiers, and annotations
rubensworks Jun 24, 2026
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Add changelog entry for the sections on triple terms and reifying tri…
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Apply suggestions from code review
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Process @TallTed's suggestion manually
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Rename triple terms section to nested triple patterns
rubensworks Aug 13, 2026
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Fix data-cite issues with reifying triple
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Clarify reference to reifying triples
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Incorporate suggestions on reifying triples by @afs manually
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Fix reifying triples being used to refer to patterns
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Fix triple patterns being asserted
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Incorporate suggestions by @hartig
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Expand Up @@ -1369,6 +1369,276 @@ <h4>rdf:type</h4>
</pre>
</section>
</section>
<section id="syntaxNestedTriplePatterns">
<h3>Nested Triple Patterns</h3>
<p> <a href="#defn_TriplePattern">Triple patterns</a> can be nested; that is, their subject or object can be
another <a href="#defn_TriplePattern">triple pattern</a>.
Such nested triple patterns are meant to match triples that contain <a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple terms</a>.
</p>
<p>To write a nested <a href="#defn_TriplePattern">triple pattern</a>
the triple pattern that it contains must be
preceded by <code>&lt;&lt;(</code>, and
followed by <code>)&gt;&gt;</code>.
</p>
<p>The example below illustrates how a <a href="#defn_TriplePattern">triple pattern</a>
can be used in the object position of another <a href="#defn_TriplePattern">triple pattern</a>.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;

SELECT ?person ?authority {
?person :familyName "Smith" .
_:anno rdf:reifies &lt;&lt;( ?person :jobTitle "Designer" )&gt;&gt; .
_:anno :accordingTo ?authority .
}
</pre>
<section id="syntaxReifyingTriples">
<h3>Shorthand to Match Reifying Triples</h3>
<p><a data-cite="RDF12-CONCEPTS#dfn-triple-term">Triple terms</a> are used
as the <a data-cite="RDF12-CONCEPTS#dfn-object">object</a> of a <a data-cite="RDF12-CONCEPTS#dfn-rdf-triple">triple</a>
with a <a data-cite="RDF12-CONCEPTS#dfn-predicate">predicate</a> of `rdf:reifies`.
Such a triple is called a <a data-cite="RDF12-CONCEPTS#dfn-reifying-triple">reifying triple</a>.
SPARQL provides a shorthand notation for writing triple patterns that are meant to match such <a data-cite="RDF12-CONCEPTS#dfn-reifying-triple">reifying triples</a>.</p>
</p>
<p class="note">Reification using triple terms is a concept distinct from the
<a data-cite="RDF12-SEMANTICS#Reif">Reification vocabulary</a> originally
defined in <a data-cite="RDF-MT#Reif">RDF Semantics</a>.
While both concepts describe a representation of an RDF triple using components,
RDF 1.2 and SPARQL 1.2 have a dedicated <a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple term</a>,
which can be used with the `rdf:reifies` predicate.
</p>
<p>The example below matches reifying triples.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;

SELECT ?person ?authority {
?person :familyName "Smith" .
&lt;&lt; ?person :jobTitle "Designer" &gt;&gt; :accordingTo ?authority .
}
</pre>
<p>The syntactic sugar of the example above expands to the following query:</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;

SELECT ?person ?authority ?id {
?person :familyName "Smith" .
_:id rdf:reifies &lt;&lt;( ?person :jobTitle "Designer" )&gt;&gt; .
_:id :accordingTo ?authority .
}
</pre>
<p>This shorthand notation for matching reifying triples
also allows the <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a>
of these reifying triples to be matched. This is done by placing
a variable, IRI, or blank node after a tilde (<code title="tilde">~</code>).
As shown in the example above; if no reifier is explicitly mentioned,
then a new blank node is minted for as reifier within the scope of this query.
</p>
<p class="note"><a href="#rReifiedTriple"><code>ReifiedTriple</code>'s</a> may be nested,
like
<br/>`&lt;&lt; ?subject1 :predicate1 &lt;&lt; :subject2 :predicate2 :object2 &gt;&gt; ~ :IRIREF1 &gt;&gt;`<br/>
or <br/>`&lt;&lt; :subject4 :predicate4 &lt;&lt; :subject3 :predicate3 ?object3 ~ :IRIREF3 &gt;&gt; &gt;&gt;`.
</p>
<p>The example below matches reifying triples with a variable to match the reifier.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;

SELECT ?person ?authority ?id {
?person :familyName "Smith" .
&lt;&lt; ?person :jobTitle "Designer" ~ ?id &gt;&gt; :accordingTo ?authority .
}
</pre>
<p>The syntactic sugar of the example above expands to the following query:</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX rdf: &lt;http://www.w3.org/1999/02/22-rdf-syntax-ns#&gt;

SELECT ?person ?authority ?id {
?person :familyName "Smith" .
?id rdf:reifies &lt;&lt;( ?person :jobTitle "Designer" )&gt;&gt; .
?id :accordingTo ?authority .
}
</pre>
<p class="note">Note the subtle difference in syntax between the syntactic sugar of
the <a href="#rReifiedTriple"><code>ReifiedTriple</code></a> (i.e., `&lt;&lt; ... >>`)
and the regular <a href="#rTripleTerm"><code>TripleTerm</code></a> (i.e., `&lt;&lt;( ... )>>`).</p>
</section>
<section id="syntaxAnnotation">
<h3>Annotation Syntax</h3>
<p>SPARQL also defines <dfn data-lt="annotation-syntax">annotation syntax</dfn>
as a shortcut form for matching both reified and asserted triples with a
<a href="#defn_TriplePattern">triple pattern</a>.
An annotation can be used to simultaneously match an asserted triple,
via an explicit or implicit identifier,
and have that triple pattern be the
<a data-cite="RDF12-CONCEPTS#dfn-subject">subject</a> or
<a data-cite="RDF12-CONCEPTS#dfn-object">object</a> of further triple patterns.
If explicitly identified, the same <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> can then be used as the
<a data-cite="RDF12-CONCEPTS#dfn-subject">subject</a> or
<a data-cite="RDF12-CONCEPTS#dfn-object">object</a> of additional
triple patterns and/or <a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple terms</a>.
</p>
<p>Like a <a href="#rReifiedTriple"><code>ReifiedTriple</code></a>,
the annotation syntax uses a <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> — written as either a
<a href="#rVar">variable</a>, an <a href="#riri">IRI</a>, or a <a href="#rBlankNode">blank node</a>,
preceded by a tilde (<code title="tilde">~</code>) —
to identify the
<a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple term</a> being reified.
However, while the
<a href="#rReifiedTriple"><code>ReifiedTriple</code></a> syntax
may contain at most one <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a>, the annotation syntax may contain
any number of <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifiers</a>. Each <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> causes a corresponding
reifying triple to be produced.
</p>
<p>A <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> can be followed by an annotation block.
If a <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> is not followed by an annotation block, it is treated
analogously to a
<a href="#rReifiedTriple"><code>ReifiedTriple</code></a>
without additional annotations.
If an annotation block is not immediately preceded by a <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a>,
a fresh RDF blank node is allocated to serve as the <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a> of the
<a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple term</a>.
</p>
<p class="note">The annotation syntax is a syntactic shortcut in SPARQL.
The RDF Abstract Syntax [[RDF11-CONCEPTS]] does not
distinguish how the triples were written.</p>
<p>The example below shows an annotated triple pattern with an explicit reifier.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority {
?person :name "Alice" ~ :t {| :statedBy ?authority ; :recorded "2021-07-07"^^xsd:date |} .
}
</pre>
<p>The syntactic sugar of the annotation syntax in the example above expands to the following query:</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority {
?person :name "Alice" .
&lt;&lt; ?person :name "Alice" ~ :t &gt;&gt; :statedBy ?authority ;
:recorded "2021-07-07"^^xsd:date .
}
</pre>
<p>If we fully expand this query to use <a href="#rTripleTerm"><code>TripleTerm</code>'s</a> instead of reifiers,
the query is expanded to the following:</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority {
?person :name "Alice" .
:t rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
:t :statedBy ?authority .
:t :recorded "2021-07-07"^^xsd:date .
}
</pre>
<p>The example below shows an annotated triple pattern with an implicit reifier, for which a fresh blank node is allocated.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority {
?person :name "Alice" {| :statedBy ?authority ; :recorded "2021-07-07"^^xsd:date |} .
}
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</pre>
<p>An <a href="#rAnnotation"><code>Annotation</code></a>
may include any number of annotation blocks. If such blocks are not
immediately preceded by explicit <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifiers</a>, each block is associated
with a fresh blank node allocated as its <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a>, as seen in the example below.</p>
Comment thread
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<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority1 ?authority2 {
?person :name "Alice"
{| :statedBy ?authority1 ; :recorded "2021-02-01"^^xsd:date |}
{| :statedBy ?authority2 ; :recorded "2021-07-07"^^xsd:date |} .
}
</pre>
<p>The query above will be fully expanded to the query below, where <code>_:b0</code> and <code>_:b1</code> stand for fresh RDF blank nodes.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person ?authority1 ?authority2 {
?person :name "Alice" .
_:b0 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
_:b0 :statedBy ?authority1 .
_:b0 :recorded "2021-02-01"^^xsd:date .
_:b1 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
_:b1 :statedBy ?authority2 .
_:b1 :recorded "2021-07-07"^^xsd:date .
}
</pre>
<p>The annotation syntax may also contain multiple explicit
<a data-cite="RDF12-CONCEPTS#dfn-reifier">reifiers</a> without annotation blocks, as shown in the example below. Each such <a data-cite="RDF12-CONCEPTS#dfn-reifier">reifier</a>
causes a corresponding reifying triple to be produced.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person {
?person :name "Alice" ~ :stmt1 ~ :stmt2 .
}
</pre>
<p>The query above will be fully expanded to the query below.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person {
?person :name "Alice" .
:stmt1 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
:stmt2 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
}
</pre>
<p>The annotation syntax could also contain multiple explicit
<a data-cite="RDF12-CONCEPTS#dfn-reifier">reifiers</a> with annotation blocks, as shown in the example below.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person {
?person :name "Alice"
~ :stmt1 {| :statedBy ?authority1 |}
~ :stmt2 {| :statedBy ?authority2 |} .
}
</pre>
<p>The query above will be fully expanded to the query below.</p>
<pre class="query nohighlight">
VERSION "1.2"
PREFIX : &lt;http://example/&gt;
PREFIX xsd: &lt;http://www.w3.org/2001/XMLSchema#&gt;

SELECT ?person {
?person :name "Alice" .
:stmt1 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
:stmt1 :statedBy ?authority1 .
:stmt2 rdf:reifies &lt;&lt;( ?person :name "Alice" )&gt;&gt; .
:stmt2 :statedBy ?authority2 .
}
</pre>
</section>
</section>
<section id="syntaxVersionAnnouncement">
<h3>Version Announcement</h3>
<p>To cope with the language evolution of SPARQL,
Expand Down Expand Up @@ -13034,7 +13304,9 @@ <h2>Changes between SPARQL 1.1 Query Language and SPARQL 1.2 Query Language</h2>
Normative changes:
<ul>
<li>Update grammar for triple terms, reifiers, reified triples, annotation syntax, and triple term functions
in <a href="#sparqlGrammar" class="sectionRef"></a></li>
in <a href="#sparqlGrammar" class="sectionRef"></a> and explain them
in <a href="#syntaxNestedTriplePatterns" class="sectionRef"></a>
and <a href="#syntaxReifyingTriples" class="sectionRef"></a></li>
<li>Add functions related to <a data-cite="RDF12-CONCEPTS#dfn-triple-term">triple terms</a> to
<a href="#func-triple-terms" class="sectionRef"></a>:
`TRIPLE`, `isTRIPLE`, `SUBJECT`, `PREDICATE`, `OBJECT`</li>
Expand Down
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