Why my ontology is full?

If you have read some about OWL you know there is three sublanguages of OWL Lite, DL and full, being the Lite the less expressive, and the FULL the most expressive[1]. So why we don’t use the OWL FULL? The problem is OWL FULL isn’t decideable, so we can’t use reasoners, this is a problem, a big problem, so in this posts I will try to say what are the features or restrictions that makes our Ontology FULL.

Metaclass: Metaclass is a class whose instances are classes. This feature can be useful in many applications, but if you use it you can’t use a reasoner. When I have to use metaclass I try to separate my models, this is an important tip, like in other disciplines in Computer Science separation of concers is always a good idea.

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What I can do when I need the metaclasses and at the same time I like to preserve decidability of Model, is to create metaclasses and classes in different OWL files and later create another file that import both and create the relation of instantiation. In this way you can use some reasoner capacity over the Model that contain the classes if is needed, but you can track the metaclasses it is instantiating usingn the three OWL files.

Transitive and Functional Relations:

Another feature that can leads to OWL-FULL is the transitive relations. You CANNOT restrict cardinality of a transitive relations or its inverse. Hence we can’t neither set a relation as transitive and Functional at the same time nor set a restriction for a class that set a cardinality for that property.

Let-me explain why:

Let’s assume instances A, B and B, and properties P and its inverse IP.

P(A,B) and P(B,C), than IP(B,A) and IP(C,B)

If we say that P is transitive than we are also defining:

P(A,C) and IP(C,A).

Remember, defines the P(A,B) or IP(B,A) is the same, hence why it is not possible define the relation cardinality nor its inverse.

If this information it’s useful for you but think it’s not clear, let me know.

[1] – http://www.w3.org/TR/owl-features/