Add missing comparison operators for triple terms (#289)

* Add missing value comparison operators for triple terms

* Support triple terms in ORDER BY

* Fix links to compareTripleTerm

Co-authored-by: Olaf Hartig <[email protected]>

* Apply suggestions from code review

Co-authored-by: Olaf Hartig <[email protected]>

* Link to SUBJECT, PREDICATE, and OBJECT functions

* Remove obsolete sentence about triple terms in operator mapping table

* Use term1/2 instead of A/B in func-compareTripleTerm

* Clarify next step in func-compareTripleTerm

* Apply suggestions from code review

Co-authored-by: Ted Thibodeau Jr <[email protected]>

* Fix formatting of compareTripleTerm

* Require relative ordering for IRIs and bnodes in compareTripleTerm

* Add comparison operators for triple terms to changelog

* Update spec/index.html

Co-authored-by: Ted Thibodeau Jr <[email protected]>

* Update spec/index.html

Co-authored-by: Ted Thibodeau Jr <[email protected]>

* Update spec/index.html

Co-authored-by: Ted Thibodeau Jr <[email protected]>

* Remove triple term comparison from operator mapping table

* Add example on undefined ordering of triple terms

* Remove explicit section references

* Update spec/index.html

---------

Co-authored-by: Olaf Hartig <[email protected]>
Co-authored-by: Ted Thibodeau Jr <[email protected]>

Author: 3 people

spec/index.html

@@ -3672,8 +3672,8 @@ <h3>ORDER BY</h3>
             </pre>
           </div>
         </div>
-        <p>The <a href="#op_lt">"&lt;" operator</a> (see the <a href="#OperatorMapping">Operator
-            Mapping</a> and <a href="#operatorExtensibility">17.3.1 Operator Extensibility</a>) defines
+        <p>The <a href="#op_lt">"&lt;" operator</a> (see the <a href="#OperatorMapping">operator
+            mapping</a> and <a href="#operatorExtensibility">operator extensibility</a>) defines
           the relative order of pairs of <code>numerics</code>,
           <code>xsd:strings</code>, <code>xsd:booleans</code> and <code>xsd:dateTimes</code>. Pairs of
           IRIs are ordered by comparing them as literals with datatype <code>xsd:string</code>.</p>
@@ -3684,8 +3684,10 @@ <h3>ORDER BY</h3>
           <li>Blank nodes</li>
           <li>IRIs</li>
           <li>RDF literals</li>
+          <li>Triple terms</li>
         </ol>
-        <p>SPARQL does not define a total ordering of all possible RDF terms. Here are a few examples
+        <p>SPARQL does not define a total ordering of all possible RDF terms. Implementations may
+          define total ordering through <a href="#operatorExtensibility">operator extensibility</a>. Here are a few examples
           of pairs of terms for which the relative order is undefined:</p>
         <ul>
           <li>"a" and "a"@en_gb (a literal with datatype <code>xsd:string</code> and a literal with a language tag)</li>
@@ -3695,6 +3697,7 @@ <h3>ORDER BY</h3>
           <li>"1"^^my:integer and "2"^^my:integer (two unsupported datatypes)</li>
           <li>"1"^^xsd:integer and "2"^^my:integer (a supported datatype and an unsupported
             datatype)</li>
+          <li>&lt;&lt; :person1 foaf:name "Bob" &gt;&gt; and &lt;&lt; :person2 foaf:name "Alice" &gt;&gt; (two triple terms)</li>
         </ul>
         <p>This list of variable bindings is in ascending order:</p>
         <div class="result">
@@ -12703,6 +12706,7 @@ <h2>Changes between SPARQL 1.1 Query Language and SPARQL 1.2 Query Language</h2>
                 <li>Update references to XPath from 2.0 to 3.1</li>
                 <li>Define `EBV` as a functional form.</li>
                 <li>Forbid duplicated variables in `VALUES`.</li>
+                <li>Add in-between term type ORDER BY support for triple terms in <a href="#modOrderBy" class="sectionRef"></a>.</li>
             </ul>
         </li>
         <li>