<rdf:RDF
    xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
    xmlns:in="http://www.example.org/instance#"
    xmlns:ex="http://www.example.org/schema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#" > 
  <rdf:Description rdf:about="http://www.example.org/instance#a">
    <ex:p rdf:resource="http://www.example.org/instance#b"/>
  </rdf:Description>
  <rdf:Description rdf:about="http://www.example.org/instance#c">
    <ex:p rdf:resource=""/>
  </rdf:Description>
</rdf:RDF>






