Make references to RDF Schema non-normative (#169)

Author: pfps

spec/index.html

@@ -103,7 +103,7 @@
 <section id='abstract'>
   <p>  This document describes a precise semantics for
     [[[RDF12-CONCEPTS]]] [[RDF12-CONCEPTS]]
-    and [[[RDF12-SCHEMA]]] [[RDF12-SCHEMA]].
+    and [[[RDF12-SCHEMA]]] [[?RDF12-SCHEMA]].
     It defines a number of distinct entailment regimes and corresponding patterns of entailment.
     It is part of a suite of documents which comprise the full specification of RDF 1.2.</p>
 </section>
@@ -1241,7 +1241,7 @@ <h4>Patterns of RDF entailment</h4>
 <section id="rdfs_interpretations">
   <h2>RDFS Interpretations</h2>
 
-  <p>RDF Schema [[RDF12-SCHEMA]]
+  <p>RDF Schema [[?RDF12-SCHEMA]]
     extends RDF to a larger vocabulary
     with more complex semantic constraints:</p>