Ontology components

Most ontologies describe individuals (instances), classes (concepts), attributes, and relations.

Examples of formal extensional ontologies are BORO, ISO 15926 and the model in development by the IDEAS Group.

If that is not the case, then you would have either a taxonomy (if hyponym relationships exist between concepts) or a controlled vocabulary.

The full expression of that fact then becomes: This tells us that the Explorer is the model that replaced the Bronco.

The addition of the is-a-subclass-of relationships creates a taxonomy; a tree-like structure (or, more generally, a partially ordered set) that clearly depicts how objects relate to one another.

In such a structure, each object is the 'child' of a 'parent class' (Some languages restrict the is-a-subclass-of relationship to one parent for all nodes, but many do not).

If we introduce meronymy relationships to our ontology, the hierarchy that emerges is no longer able to be held in a simple tree-like structure since now members can appear under more than one parent or branch.

For example, in the domain of automobiles, we might need a made-in type relationship which tells us where each car is built.