& ...; in RDF / XML is a standard RDF prefix expression?

Question

I downloaded WordNet2.0 fullset. There are elements in the RDF / XML document wnfull.rdfs that use, for example, &wn20schema;AdverbSynsetattribute values ​​(where URIs are expected). I know how they are commonly used #, url/and value:, but what is this &...;?

<rdfs:Class rdf:about="&wn20schema;Synset" />  
<rdfs:Class rdf:about="&wn20schema;AdjectiveSynset" />  
<rdfs:Class rdf:about="&wn20schema;AdjectiveSatelliteSynset" />  
<rdfs:Class rdf:about="&wn20schema;AdverbSynset" />  

Answer 1

&wn20schema; is an entity reference.

The XML document must contain or indicate its extension, i.e. sort of

<!ENTITY wn20schema "…">

&wn20schema;will be replaced by ….

Literature:

• XML 1.0: http://www.w3.org/TR/2008/REC-xml-20081126/#sec-physical-struct
  • . .
• XML 1.1: http://www.w3.org/TR/2006/REC-xml11-20060816/#sec-physical-struct
  • . .