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
- 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
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.