Support for subProperty hierarchies

[psiotwo]

Subproperty hierarchies are quite common in data and are one of the fancy features that might well distinguish RDFS ontologies from Java object model.

As a user I want to have an option to operate with a subproperty hierarchy within a single JOPA attribute. For example, having a skos:broader property, I need to have an attribute which will be able to CRUD SKOS:broader and its subproperties (like rdfs:subClassOf, ?:partOf, rdf:type, etc.).

Some ideas for discussion:

• a custom type - @OWLObjectProperty(SKOS:broader, includeSubProperties=true) private Hierarchy broader (similarly to MultilingualString), which will be configured by a property (the root) and will dynamically fetch its hierarchy.
• a custom filter on @properties - @Properties(properties={SKOS:broader}, includeSubProperties=true) private Map<IRI,Set<IRI>> - configured by a property selector.