DL –Safe SWRL Rules on OWL DL Ontologies with PelletDL –Safe SWRL Rules on OWL DL Ontologies with Pellet

Here is a simple example to understand the meaning of DL Safety.

In a DL Safe rule execution,only explicitly named individuals are bound to the variables in the rule.

Lets say we have a transitive object property named ancestorOf.

Can we simulate this transitivity using a DL-Safe SWRL rule rather than defining the ancestorOf property as transitive?

At the first glance it seems possible since transitivity is simply:transitive_property(?X,?Y),transitive_property(?Y,?Z) –>transitive_property(?X,?Z)

To illustrate more clearly lets create the following ontology. I used Protégé 4.0 and Pellet Reasoner Plug-in 1.0 for Protégé.

As expected the inferred class hierarchy is:

Now remove the transitive characteristic of ancestorOf. And Add the rule shown below.

Now classify the ontology again and look at the inferred class hierarchy.

In the first case the inference mechanism determines that AncestorOfOlympian is a super class of AncestorOfChronos.

Because Chronos is already an ancestor of some unknown individual of type Olympian and ancestorOf is transitive,then ancestor of Chronos is already an ancestor of Olympian.

Also Uranus is listed as an instance of AncestorOfOlympian.

In the second case ,since there is no individual of Olympian is present,the inferences mentioned above can not be done.

Note that if we add an instance of Olympian (e.g. Zeus) and make Chronos ancestor of Zeus then Uranus is listed as an instance of AncestorOfOlympian however the inferred class hierarchy remains unchanged.

P.S. This example is a simplified version of weblog entry of Bijan Parsia.