Delete the obsolete OMF metadata ontology.

[NicolasRouquette]

The OMF metadata ontology was a precursor to the current OML:

OWL Classes annotated omf:isAbstract=false correspond to concrete OML metaclasses.
For example:

omf:ModelEntityAspect corresponds to oml:Aspect
omf:ModelEntityConcept corresponds to oml:Concept
omf:ModelEntityReifiedRelationship corresponds to oml:ReifiedRelationship

Since the OWL2-DL + SWRL representation of, e.g., an omf:ModelEntityReifiedRelationship involves a complex pattern of multiple OWL2-DL entities, including:

• an OWL2-DL Class representing the omf:ModelEntityReifiedRelationship as a class;
• an OWL2-DL ObjectProperty representing the omf:ModelEntityReifiedRelationship as a relation;
• a pair of OWL2-DL ObjectProperties representing the domain and range of that relation;
• a SWRL rule encoding the logical entailment of a relationship fact from assertions about an instance of the class and of the domain/range relationships.

Recognizing this pattern is non-trivial and error prone because one has to be careful about discerning the use of OWL2-DL Class for representing OML/OMF Aspects, Concepts, ReifiedRelationships or StructuredDatatypes as well as discerning the use of OWL2-DL ObjectProperty for representing OML/OMF ReifiedRelationships (as a property, or its domain or its range or its inverse) or an OML/OMF UnreifiedRelationship or an OML/OMF StructuredDataProperty or an OML/OMF EntityStructuredDataProperty.

The OMF metadata ontology provided an OWL2-DL instance-level representation that was simpler to parse because each individual was classified in terms of the kind of OML/OMF thing it is representing and related explicitly with other OML/OMF individuals via OML/OMF object properties.

The definition of OML as an explicit language now alleviates the need for the OMF metadata ontology.