An ontology defines the concepts and relationships used to describe and represent an area of knowledge (subject matter). It provides:

• A vocabulary
• A shared language

An ontology is defined using constructs for:

Concepts: classes Relationships: properties (object and data) Rules: axioms and constraints Instances of concepts: individuals (data)

Ontologies can be used for many purposes, including enterprise integration, information retrieval, network management and information interchange on the World Wide Web. Ontologies can contain business rules and definitions which are processed and enforced at run time by standard inferencing components. This enables application code for semantic (ontology-based) systems to be thinner and more generic.