Clarify relationship of JSON-LD and RDF

according the resolutions made in the 2013-06-11 JSON-LD telecon. See http://json-ld.org/minutes/2013-06-11

This addresses #222

spec/latest/json-ld/index.html

@@ -217,12 +217,14 @@ <h2>How to Read this Document</h2>
 
     <ul>
       <li>Software developers who want to encode Linked Data in a variety of
-        programming languages that can use JSON.</li>
+        programming languages that can use JSON</li>
       <li>Software developers who want to convert existing JSON to JSON-LD.</li>
       <li>Software developers who want to understand the design decisions and
-        language syntax for JSON-LD.</li>
+        language syntax for JSON-LD</li>
       <li>Software developers who want to implement processors and APIs for
-        JSON-LD.</li>
+        JSON-LD</li>
+      <li>Software developers who want to generate or consume Linked Data, an
+        RDF graph, or an RDF Dataset in a JSON syntax</li>
     </ul>
 
     <p>A companion document, the JSON-LD Processing Algorithms and API specification
@@ -268,6 +270,13 @@ <h1>Design Goals and Rationale</h1>
      esoteric use case, we chose not to support the use case. While Zero Edits is
      a design goal, it is not always possible without adding great complexity
      to the language. We should focus on simplicity when possible.</dd>
+    <dt>Usable as RDF syntax</dt>
+    <dd>JSON-LD was designed to be usable directly as JSON, with no knowledge of RDF,
+      but was designed also to be usable as RDF for use with other Semantic Web
+      technologies like SPARQL. People intending to use JSON-LD with RDF tools will
+      find it can be used as another RDF syntax, like Turtle. Complete details of
+      how JSON-LD relates to RDF can be found in
+      <a class="sectionRef" href="#relationship-to-rdf"></a>.</dd>
   </dl>
 </section>
 
@@ -3129,10 +3138,14 @@ <h2>Context Definitions</h2>
 <section class="appendix normative">
   <h2>Relationship to RDF</h2>
 
-  <p>The RDF data model, as outlined in [[RDF11-CONCEPTS]], is an abstract syntax for
-    representing a directed graph of information. It is a subset of
-    <tref title="JSON-LD data model">JSON-LD's data model</tref> with a few
-    additional constraints. The differences between the two data models are:</p>
+  <p>JSON-LD is a
+    <tref href="http://www.w3.org/TR/rdf11-concepts/#dfn-concrete-rdf-syntax">concrete RDF syntax</tref>
+    as described in [RDF11_CONCEPTS]. Hence, a JSON-LD document is both an
+    RDF document and a JSON document and correspondingly represents both an
+    instance of the RDF data model and an instance of the JSON-LD data model.
+    RDF's data model is a subset of <tref title="JSON-LD data model">JSON-LD's data model</tref>
+    with a few additional constraints. The differences between the two data
+    models are:</p>
 
   <ul>
     <li>In JSON-LD <tref title="graph name">graph names</tref> can be
@@ -3163,9 +3176,9 @@ <h2>Relationship to RDF</h2>
     <tref title="property">properties</tref> to <tref title="IRI">IRIs</tref>,
     minting new "Skolem IRIs" as per
     <cite><a href="http://www.w3.org/TR/rdf11-concepts/#section-skolemization">Replacing Blank Nodes with IRIs</a></cite>
-    of [[RDF11-CONCEPTS]]. A complete description of the algorithms to convert
-    from RDF to JSON-LD and from JSON-LD to RDF is included in the JSON-LD
-    Processing Algorithms and API specification [[JSON-LD-API]].</p>
+    of [[RDF11-CONCEPTS]]. The normative algorithms for interpreting JSON-LD as RDF
+    and serializing RDF as JSON-LD are specified in the
+    JSON-LD Processing Algorithms and API specification [[JSON-LD-API]].</p>
 
   <p>Even though JSON-LD serializes
     <tref href="http://www.w3.org/TR/rdf11-concepts/#dfn-rdf-dataset">RDF Datasets</tref>, it can