In OWL, complex classes can be defined using Description Logic operators, such as owl:unionOf, owl:disjointWith, owl:intersectionOf etc. In v0.3, F-OWL has limited support for reasoning over these Description Logic operators.

In this section, we demonstrate the support for determining individuals of a complex class which is defined by using the owl:intersectionOf construct (intersections of named classes only).

In our example ontology (animals.owl), the following ontology is defined.

<owl:Class rdf:ID="TwoLeggedThing"/>
<owl:Class rdf:ID="TwoLeggedPerson">
  <owl:intersectionOf rdf:parseType="Collection">
    <owl:Class rdf:about="#Person"/>
    <owl:Class rdf:about="#TwoLeggedThing"/>
  </owl:intersectionOf>
</owl>
<TwoLeggedPerson rdf:ID="Harry"/>

This ontology defines a complex class called animals:TwoLeggedPerson as the intersection of two classes -- animals:TwoLeggedThing and animals:Person. An individual animals:Harry is a type of animals:TwoLeggedPerson.

From this ontology, the following query in F-OWL will return animals:Harry is of both type animals:TwoLeggedThing and animals:Person:

animals_Harry : animals_TwoLeggedThing.

animals_Harry : animals_Person.

NOTE: the above example cannot be demonstrated in v0.3 due to a system bug in the underlying Flora-2/XSB implementation (05.11.2003).