Add property foaf:homepage to entities

public/instance/schema/shared-dc.rnc

 # Wiederverwendbare Definition von Eigenschaften aus Dublin Core Qualified
 #
 # Autor: David Maus <maus@hab.de>
-# Timestamp: <2019-01-16 12:27:31 maus>
+# Timestamp: <2019-01-16 12:29:00 maus>
 #
 
 namespace dct = "http://purl.org/dc/terms/"
+namespace foaf = "http://xmlns.com/foaf/0.1/"
 namespace rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
 namespace owl = "http://www.w3.org/2002/07/owl#"
 namespace skos = "http://www.w3.org/2004/02/skos/core#"
@@ -54,17 +55,25 @@ property.label =
     & text
    }
 
+property.homepage =
+   element foaf:homepage {
+      attribute rdf:resource { xsd:anyURI }
+    & empty
+   }
+
 model.Entity = ( model.internalEntity | model.externalEntity )
 
 model.internalEntity =
    attribute rdf:about { xsd:anyURI }?
  & property.label
+ & property.homepage
 
 model.externalEntity =
    element owl:sameAs {
       attribute rdf:resource { xsd:anyURI }
    }*
  & property.label
+ & property.homepage
 
 model.rdfLiteral =
    attribute rdf:datatype { xsd:anyURI }?