In philosophy, ontology (from the Greek , genitive : of being (part. of : to be) and -λογία: science, study, theory) is the study of being or existence. This most fundamental branch of metaphysics seeks to describe or posit the basic categories and relationships of being or existence to define entities and types of entities within its framework. Ontology can be said to study conceptions of reality.
Some philosophers, notably of the Platonic school, contend that all nouns refer to entities. Other philosophers contend that some nouns do not name entities but provide a kind of shorthand way of referring to a collection (of either objects or events). In this latter view, mind, instead of referring to an entity, refers to a collection of mental events experienced by a person; society refers to a collection of persons with some shared characteristics, and geometry refers to a collection of a specific kind of intellectual activity. Any ontology must give an account of which words refer to entities, which do not, why, and what categories result. When one applies this process to nouns such as electrons, energy, contract, happiness, time, truth, causality, and God, ontology becomes fundamental to many branches of philosophy.
Classification :: Knowledge Retrieval
Ontology :: Metaphysics
Logic and Ontology :: Philosophy of Logic

Adaptive Path - Metadata for the Masses - Discussion of the promise and problems of classification systems created by nonprofessionals.
Meta Description: [ A User Experience design and consulting firm that unites theory and practice to advance the art of user experience design while helping clients make better business decisions. Located in San Francisco, California, USA. ]
Buffalo Ontology Site - Large collection of links and papers about Contemporary Ontology, History of Ontology and Ontological Engineering. From the Department of Philosophy, State University of New York.
CO-ODE - Collaborative Open Ontology Development Environment is a project led by the Medical Informatics Group at the University of Manchester.
Meta Description: [ CO-ODE. Collaborative Open Ontology Development Environment project from the Medical Informatics Group at the University of Manchester ]
European Centre for Ontological Research (ECOR) - ECOR represents a new approach in applying ontology to a variety of problems in information science and related areas, by coordinating institutions, organisations and companies working in the field.
Knowledge-Base and Ontology Projects Worldwide - A catalog of links to projects, tools, and events.
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On-To-Knowledge - A project of the European Information Society Technologies, under 5th Framework Program (1999-2002). The project develops knowledge management methods and tools, based on ontology sharing and reuse.
Ontologies Come of Age - Paper by Deborah L. McGuinness discussing ontologies and requirements for their effective use on the web. [2002]
Ontologies For Education - A topic-map driven portal focused on application of ontologies and similar technologies to educational domains.
Ontology Engineering Background - Overview of methodologies, papers and people.
Ontology Engineering: a survey and a return on experience - Research report by INRIA, presenting the state of the art of engineering techniques and a project description. (downloadable PDF)
Meta Description: [ Gandon, Fabien ]
Ontology is Overrated: Categories, Links, and Tags - Clay Shirky explores online categorization, contrasting ontologies with folksonomies.
Meta Description: [ Clay Shirky's writings about the Internet, including Economics and Culture, Media and Community, Open Source ]
Ontoweb - The community site for Ontoweb, a European Union founded project about Ontology-based information exchange for knowledge management and electronic commerce.
OWL Web Ontology Language Reference - Detailed description of the OWL W3C specification.
Principles of ontology - Mailing list archive. Some basic definitions by John Sowa.
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Wired News: Folksonomies Tap People Power - A growing number of sites whose content is user-created rely on tagging systems, also known as folksonomies, to organize the data.
WonderWeb : Ontology Infrastructure for the Semantic Web - A project aiming at large-scale deployment of ontologies as the foundation for the Semantic Web.
You're It - A weblog about social tagging.
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