Ontologies Info

Ontologies describe the following:

• An entity, which represents a category of objects. For example, in an ontology that describes cultural objects an entity could be “archaeological sites”
• An attribute, which represents characteristics of an entity. In the above mentioned cultural ontology, attributes for entity “archaeological sites” could include “age”, “location”, etc.
• A relationship, which shows how entities are linked to each other. A common relationship in ontologies is the “is a” one. For example, a temple “is a” archaeological site.

Deciding whether something should be represented by an attribute or an entity takes careful consideration including the ways in which this items will be used. Some general rules of thumb follow:

• If a concept has significant properties and/or describes classes of objects with an autonomous existence, it is appropriate to represent it as an entity.
• If a concept has a simple structure, and has no relevant properties associated with it, it is convenient to represent it with an attribute of another concept to which it refers.
• If a concept provides a logical link between two (or more) entities, it is convenient to represent it with a relationship.
• If one or more concepts are particular cases of
  another concept, it is convenient to represent them
  in terms of a generalization relationship.