------------------------------------------------------------------
<?xml version="1.0"?>
<rdf:RDF
   xmlns:rdf=" http://www.w3.org/1999/02/22-rdf-syntax-ns#"
   xmlns:xsd="http://www.w3.org/2001/XMLSchema#"
    xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
   xmlns:owl="http://www.w3.org/2002/07/owl#">

 <owl:Class rdf:about="#Grandad">
   <rdfs:comment
rdf:datatype="http://www.w3.org/2001/XMLSchema#string">old</rdfs:comment>
 </owl:Class>

 <owl:Class rdf:about="#Dad">
   <rdfs:subClassOf>
     <owl:Class rdf:about="#Grandad"/>
   </rdfs:subClassOf>
 </owl:Class>

 <owl:Class rdf:ID="Son">
   <rdfs:subClassOf rdf:resource="#Dad"/>
 </owl:Class>

 <owl:Class rdf:ID="Daughter">
   <rdfs:subClassOf rdf:resource="#Dad"/>
 </owl:Class>

However as you can see the relationship is part of each element, as
opposed to having the element nested within each other based on their
relationship.

If the relationships were going downwards it would be easy, i.e. The
"Grandad" class would state what classes are inheriting from it,
however as inheritance and classes don't work this way, i don't know
how these relationships can be converted to a hierarchy structure such
as:
<Grandad>
 <Dad>
   <Son>
   </Son>
   <Daughter>
   </Daughter>
 </Dad>
</Grandad>

I am not too concerned with the form of presentation, only how to
backtrack the Classes based on the relationship.
For example to be able to create something like the below:
<div>
   Grandad
   <div>
       Dad
       <div>
           Son
       </div>
       <div>
           Daughter
       </div>
   </div>
</div>

Thanks in advance
John