what is an ontology

An ontology is a formal description of knowledge as a set of concepts within a domain and the relationships that hold between them. It is a way of showing the properties of a subject area and how they are related, by defining a set of terms and relational expressions that represent the entities in that subject. Ontologies are used in information science to represent and define categories, properties, and relations between concepts, data, or entities that pertain to one, many, or all domains of discourse. They are also used in computer science to enable the modeling of knowledge about some domain, embody the results of academic research, and offer an operational method to put theory to practice in database systems. Ontologies are part of the W3C standards stack for the Semantic Web, in which they are used to specify standard conceptual vocabularies in which to exchange data among provide services for answering queries, publish reusable knowledge bases, and offer services to facilitate interoperability across multiple, heterogeneous systems and databases.