comments Sandro included
authorGuus Schreiber <>
Mon, 03 Feb 2014 23:43:48 +0100
changeset 1798 466e2c9bdd73
parent 1797 9bc677d5ffbe
child 1799 cae0e05c5757
comments Sandro included
--- a/rdf-primer/index.html	Mon Feb 03 23:14:38 2014 +0100
+++ b/rdf-primer/index.html	Mon Feb 03 23:43:48 2014 +0100
@@ -728,7 +728,7 @@
 <p>Lines 8-12 show how Turtle provides a shorthand for a set of
 triples with the same subject. Lines 9-12 specify the predicate-object
-part of triples that habe <code>&lt;;</code> as
+part of triples that have <code>&lt;;</code> as
 their subject. The semicolons at the end of lines 9-11 indicate that
 the predicate-object pair that follows it is part of  
 a new triple that uses the most recent subject shown in the data &#8212; in 
@@ -923,8 +923,10 @@
       <dd>RDF/XML [[RDF-SYNTAX-GRAMMAR]] (<a
       href="#rdf-xml-example">single-graph example</a>)
       provides an XML syntax for RDF
-      graphs. RDF/XML was the only normative syntax for RDF when RDF
-      1.0 was published in 2004. </dd>
+      graphs. When RDF was original developed in the late 1990s, this was its 
+      only syntax, and some people still call this syntax "RDF". In 2001, a 
+      precursor to Turtle called "N3" was proposed, and gradually the other 
+      syntaxes listed here have been adopted and standardizedR. </dd>
    <p>For more information about these syntaxes consult the references.</p>
@@ -936,15 +938,53 @@
 <section id="section-semantics">
     <h2>Semantics of RDF Graphs</h2>
+    <p>An overarching goal in the use of RDF is to be able to
+    automatically merge useful information from multiple sources to
+    form a larger collection that is still coherent and useful. As a
+    starting point for this merging, all the information is conveyed
+    in the same simple style, subject-predicate-object triples, as
+    described above. To keep the information coherent, however, we
+    need more than just a standard syntax; we also need agreement
+    about the semantics of these triples. </p>
+    <p>By this point in the Primer, the reader is likely to have an
+    intuitive grasp of the semantics of RDF:</p>
+    <ol>
+      <li>The IRIs used to name the subject, predicate, and object are "global" in scope,
+    naming the same thing each time they are used.</li>
+      <li>Each triple is "true" exactly when the predicate relation actually exists between
+    the subject and the predicate.</li>
+      <li>An RDF graph is "true" exactly when all the triples in it are "true".</li>
+    </ol>
+    <p>These notions,
+    and others, are specified with mathematical precision in the RDF
+    Semantics document [RDF11-MT].</p>
+    <p>One of the benefits of RDF having these declarative semantics
+    is that systems can make logical inferences. That is, given a
+    certain set of input triples which they accept as true, systems
+    can in some circumstances deduce that other triples must,
+    logically, also be true. We say the first set of triples "entails"
+    the additional triples. These systems, called Reasoners, can also
+    sometimes deduce that the given input triples contradict each
+    other. </p> 
+    <p>Given the flexibility of RDF, where new vocabularies can be
+    created when people want to use new concepts, there are many
+    different kinds of reasoning one might want to do.  When a
+    specific kind of reasoning seems to be useful in many different
+    applications, it can be documented as an <a
+    href="">"entailment regime"</a>.
+    Several entailment regimes are specified in RDF Semantics.     For
+    technical description of some other entailment regimes and how to
+    use them with SPARQL, see [[SPARQL11-ENTAILMENT]]. 
+    Note that some 
+    entailment regimes are fairly easy to implement and reasoning can
+    be done quickly, while others require a very sophistical
+    techniques to implement efficiently. </p> 
-    <p>RDF is grounded in a formal model-theoretic semantics which is
-    specified in the RDF 
-    Semantics document [[RDF11-MT]]. This document
-    specifies truth-preserving conditions of RDF graphs as
-    well as valid derivations from RDF graphs. Such logical
-    consequences are called <a
-    href="">entailments</a>. For
-    example, consider the following two statements:</p>
+    <p>As a sample entailment, consider the following two statements:</p>
     <code>ex:bob foaf:knows ex:alice .</code>
     <code>foaf:knows rdfs:domain foaf:Person .</code>