Classifications, Taxonomies, Ontologies, Thesauri The following three terms: classifications, taxonomies and ontologies are often confused. This is caused by a trend to use the most fashionable of the three terms “ontology”.

Classification: Definition Merriam-Webster definition: systematic arrangement in groups or categories according to established criteria. An example of a classification would be the division of all plants in the classes decorative and non-decorative.

Taxonomy: Definition Longman definition: the process or a system of organizing things into different groups that show their natural relationships, especially plants or animals Meriam-Webster definition: orderly classification of plants and animals according to their presumed natural relationships A taxonomy can described as (hierarchical) classification of items created according to data internal criteria.

Ontology: Yet Another Definition "The term ontology has many meanings and shades of meaning. In the contest of this work*, we refer to what is sometimes called a "structural" ontology -- a machine readable set of definitions that create a taxonomy of classes and subclasses and relationships between them.“ * Web Ontology (WebONT) Working Group Charter at

Classifications and Taxonomies: Comparison Taxonomies are classifications that: have hierarchical structure list items that are organised according to their natural relationships

Taxonomies and Ontologies Most ontologies could be described as taxonomies + definitions + various properties and relations (rather than just taxonomic, i.e., is_a, relations)

Thesauri and Ontologies Nowadays, thesaurus most commenly means a listing of words with similar, related, or opposite meanings. "A formal definition of a thesaurus designed for indexing is: a list of every important term (single-word or multi-word) in a given domain of knowledge; and a set of related terms for each term in the list.“* "In Information Technology, a thesaurus represents a database or list of semantically orthogonal topical search keys. In the field of Artificial Intelligence, a thesaurus may sometimes be referred to as an ontology.“* Additional reading: *

Animal Kingdom Taxonomy Kingdom, class, order, genus, species Gray wolves are dogs. Dogs are carnivore. Carnivores are mammals. Mammals are animals. National Center for Biotechnology Information (US): –

Ontology Management and Maintenance Tools Protégé is a free, open source ontology editor and knowledge-base framework. Protégé ontologies can be exported into a variety of formats including RDF(S), OWL, and XML Schema. For more cf.:

Protege Tutorial Some tutorials: mcguinness.html

Some Important Existing Ontologies Cyc: Suggested Upper Merged Ontology (SUMO): WordNet Lexical reference system: Gene Ontology: Foundational, Core and Linguistic Ontologies:

Last but not Least Ontoverse: