Using Same Object Property between Multiple Classes

Question

I tried to use the same object property between multiple classes, but I got a warning that the same object property has been set multiple times as follows, can you please let me know what is wrong with that and how to solve it? Does this restrict reasoning later on (i.e. confuse the reasoner since the same object property is set multiple times)?

Thanks

Answer 1

Contrary to the comments it actually is very problematic to use the same object property between multiple classes.

What you don't see in your visualization is that in RDF/OWL, the starting point of your relation arrows is modelled as rdfs:domain and the target point of the arrows is modelled as rdfs:range.

The semantic of an OWL class is that it is a set of individuals and rdfs:domain and rdfs:range specify the domain, respectively range of a relation. That is, they specify the sets of allowed values in subject, respectively object position of a triple with that relation in the predicate position.

If you express your example in RDF Turtle it would look like this:

:hasPart rdfs:domain :ClassA, :ClassB;
         rdfs:range :ClassB, :ClassC, :ClassD.

This causes multiple problems:

Intersection

The semantic of multiple domains, respectively ranges, is the intersection of those classes, not the union!

Even if we disregard the relation between :ClassB and :ClassD, this means :hasPart is only allowed by individuals that are instances of class C and class D at the same time!

For example, lets say class A is "car", class B is "tire" and class C is "motor". Now you want to say that a car can have tires and motors but what you actually specify is that a car can only have things that are a motor and a tire at the same time!

Unwanted but allowed usage

If you fix the first problem but specifying the union instead of the intersection, it will be very messy in serialized RDF because you need a large amount of triples to represent OWL restrictions such as unions. But even if you do that, you could now connect an instance of class A with an instance of class D, which is not allowed in the image.

Solution

The solution is simple, just separate those relations, for example into :hasB, :hasC and :hasD, although in a real scenario you can probably find a more suitable naming scheme, where the "has" prefix is often not used. For example, in DBpedia, the property for the country of a city is expressed using dbo:country, not dbo:hasCountry.