From: Taxodiary -product Data Harmony- blogpost: The Meanings of Ontology

What we find is that “ontology” is a word like “facets”; it is searching for a real definition. Until the various knowledge and research communities fully coalesce, I don’t think we will know exactly what someone means by “ontology”. That means when you start a conversation with someone about an ontology it is best to first set the syntactical framework of your conversation. What do they mean when they say ontology?

Stanford University has developed an ontology software called Protégé, which people seem to either love or hate: open source software and it is available.

Protégé is a free, open source ontology editor and knowledge-base framework.

The Protégé platform supports two main ways of modeling ontologies via the Protégé-Frames and Protégé-OWL editors. Protégé ontologies can be exported into a variety of formats including RDF(S), OWL, and XML Schema. (more)

Protégé is based on Java, is extensible, and provides a plug-and-play environment that makes it a flexible base for rapid prototyping and application development. (more)