In information technology, and by extension in geomatics, an ontology is a structured set of terms and concepts representing the meaning of a field of information. According to Gruber, 1) “an ontology is a specification of a conceptualization. […] A conceptualization is an abstract, simplified view of the world that we want to represent. ” Before creating a database, it is necessary to think about how it will simplify reality to create a computer version, and thus how to define the entities and database objects, classes and categories (sets, collections, or types of objects), attributes (properties, features, characteristics or parameters that objects can have and share), relationships (links between objects) and events (changes undergone by attributes or relationships). Another way to consider an ontology is to see it as the network of concepts and the vocabulary that describes a domain. There are computer tools to help define and manage the ontology of a domain.

This definition is directly inspired by Wikipedia http://en.wikipedia.org/wiki/Ontology

1) Thomas R. Gruber, Towards Principles for the Design of Ontologies Used for Knowledge Sharing in Formal Ontology in Conceptual Analysis and Knowledge Representation, Kluwer Academic Publishers, 1993.

For further reading: http://tomgruber.org/writing/ontology-definition-2007.htm
[French: Ontologie]