<rdf:RDF 
  xmlns:rdf ="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
>
   <rdf:Description rdf:ID="TonysSpecialty">
      <rdf:type rdf:resource="#CRAB"/>
   </rdf:Description>

   <rdfs:Class rdf:ID="CRAB">
      <rdfs:subClassOf rdf:resource="#SHELLFISH"/>
   </rdfs:Class>

   <rdfs:Class rdf:ID="SHELLFISH">
      <rdfs:subClassOf rdf:resource="#SEAFOOD"/>
   </rdfs:Class>
</rdf:RDF>