Merge pull request #711 from w3c/dcat-issue710-riccardo

adding an opening sentence for the section on Dereferenceable Identifiers

dcat/index.html

@@ -2275,7 +2275,7 @@ <h3>Class: Role</h3>
 <section id="Dereferenceable-identifiers" class="informative">
     <h2>Dereferenceable identifiers</h2>
 
-    <p>DCAT should rely on persistent HTTP URIs, which are an effective way of making identifiers actionable.</p>
+    <p>The scientific and data provider communities use a number of different identifiers for publications,  authors and data. DCAT primarily relies on persistent HTTP URIs as an effective way of making identifiers actionable. Notably, quite a few identifier schemes can be encoded as dereferenceable HTTP URIs, and some of them are also returning machine-readable metadata (e.g., DOIs, ORCIDs). Regardless, data providers still might need to refer to legacy identifiers, non-HTTP dereferenceable identifiers, locally minted or third-party-provided identifiers. In these cases, [[DC11]] and [[VOCAB-ADMS]] can be of use.</p>
     <p>The property <a href="#Property:resource_identifier"><code>dct:identifier</code></a>  explicitly indicates HTTP URIs as well as legacy identifiers. In the following examples,  <a href="#Property:resource_identifier"><code>dct:identifier</code></a>  identifies a dataset, but it can similarly be used with any kind of resources.</p>
 
 <pre id="ex-identifier" class="example nohighlight turtle" aria-busy="false" aria-live="polite">