Ontology

An ontology defines the common words and concepts (meanings) used to describe and represent an area of knowledge, and so standardizes the meanings. Ontologies are used by people, databases, and applications that need to share domain information (a domain is just a specific subject area or area of knowledge, like medicine, counter terrorism, imagery, automobile repair, etc.). Ontologies include computer usable definitions of basic concepts in the domain and the relationships among them. They encode knowledge in a domain and also knowledge that spans domains. So, they make that knowledge reusable.

An ontology includes the following:

• Classes (general things) in the many domains of interest
• Instances (particular things)
• Relationships among those things
• Properties (and property values) of those things
• Functions of and processes involving those things
• Constraints on and rules involving those things

A data set describing things and their existence in the world.

Ontology defines concepts, providing a way to move towards consistency in vocabulary. It provides a working model of the entities and interactions of a particular topic, such as dentistry or anthropology. It also has a specific knowledge related to a given domain name - for example, in finance or pharmaceuticals.

In philosophy it is the study of being. As it relates to search, it is the attempt to create an exhaustive and rigorous conceptual schema about a domain. An ontology is typically a hierarchical data structure containing all the relevant entities and their relationships and rules within that domain. See also: Wikipedia: Ontology Open Directory Project, The (see DMOZ)