There is a wide variety of languages used for building ontologies. These range from simple bipartite graphs to advanced description logics. Languages vary in complexity, and can be compared on the basis of the kinds and numbers of expressions that can be created in the language.

Leading ontology languages:

• RDF

• Topic Maps

• DAML

• OIL

• Ontolingua

Basic Elements (Thesaurus):

• Broader Term (BT) - A particular term is more general than another term (?crop? is broader than ?soybeans?)

• Narrower Term (NT) ? A particular term is more specific than another (?soybeans? is narrower than ?crop?)

• Related Term (RT) ? Two terms are associated (?leaf? is related to ?plant?)

• Use For (UF) ? A particular term is the preferred term among a set of synonymous terms (use ?grower? for ?farmer?)

Thus, a thesaurus entry for the term ?soybean? might look like:

• Soybean

• BT: legume

• NT: Bragg, Cobb, ?

• RT: pod, leaf

• UF: soy

Basic Ontology Elements:

• Class: A generic concept

• Subclass: A more specific generic concept.

• Object: A particular occurrence of a generic concept

• Subclass: A class that is more specific than a particular class

• Superclass: A class that is more general than a particular class

• PartOf: An object that is part of a particular object

• Association: Two objects are related in general (other than one of the above relationships)

Advanced Ontology Elements:

• Attribute Restrictions

• Subproperties

• And/Or/Not

• Cardinality

• Axioms

• Rules

• Primitive/Defined Classes