Question

I want to check whether a property is functional or not. I tried:

ASK {
  pz:isBase owl:isInverseFunctional .
}

but it is a syntax error. How can I check whether a property is functional?

Answer 1

Try:

ASK {pz:isBase rdf:type owl:InverseFunctionalProperty}

To explain: the patterns that RDF represents, and which SPARQL queries, are triples of subject predicate object, or in other words a binary predicate. You’re thinking of a unary predicate isInverseFunctional(), but RDF doesn’t do unary predicates. Instead, that kind of type or sortal information is encoded as a binary predicate with a special predicate rdf:type, which you can think of as isKindOf or is member of the class.

So, to discover whether a resource denoting a particular predicate in your domain model is an inverse functional property, you ask whether that resource is in the class of, i.e. has rdf:type the class of all inverse functional properties or owl:InverseFunctionalProperty.