Extending properties in sub-class

What is the better way of extending (and modifying) properties inherited
from the super class? To elaborate my question I present a scenario. Think
of a "Person" and "Document" as sub-class of "Entity". Two entities could
have associations between each other, being the source and target, modeled
as below:

<owl:Class rdf:ID="Entity"/>
<owl:Class rdf:ID="#Document">
  <rdfs:subClassOf rdf:resource="#Entity"/>
</owl:Class>
<owl:Class rdf:ID="Person">
  <rdfs:subClassOf rdf:resource="#Entity"/>
</owl:Class>

<owl:Class rdf:ID="Association"/>

<owl:ObjectProperty rdf:ID="source">
  <rdfs:range rdf:resource="#Entity"/>
  <rdfs:domain rdf:resource="#Association"/>
</owl:ObjectProperty>

<owl:ObjectProperty rdf:ID="target">
  <rdfs:range rdf:resource="#Entity"/>
  <rdfs:domain rdf:resource="#Association"/>
</owl:ObjectProperty>


So far so simple, and now the problem! What if I want to have a special case
for association, Authorship, which says the "source" property MUST only be
"Person" instead of any "Entity"

<owl:Class rdf:ID="Author">
  <rdfs:subClassOf rdf:resource="#Association"/>
</owl:Class>

How to modify the property "source" for "Author" to have "Person" in its
"range" so that it doesn't effect the previous general case?


Khalid