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Ontology locked

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An Ontology is a set of explicit shared formal concepts which permits Categorization. It is used to organize or classify content (or information, or knowledge). The concepts have names (words) and definitions (meanings). They are used to talk about the content. They are MetaData.

The part of the world conceptualized or described is called the "knowledge domain." The ontology is a "knowledge representation."

The things that can be said with these concepts is called the UniverseOfDiscourse? and the humans or computer agents using them is called a CommunityOfDiscourse?. Not everything can be said, but when the concepts are formal (machine-readable), the things sayable are considered knowledge in the field of KnowledgeManagement.

An ontology is usually arranged hierarchically, like a Taxonomy. The main branches are the fundamental categories. If they are named, the core concepts or terms become a ControlledVocabulary. When arbitrary relations are allowed between terms, a taxonomy becomes a Thesaurus?.

Explicit means the concepts are defined clearly; formal usually means defined in an unambiguous way. These defined concepts are then used to describe objects (content elements) or the relations between objects. When we add definitions to a vocabulary, we call it a glossary, lexicon, or dictionary.

A taxonomy is syntactic (structural). An ontology is semantic.

The descriptions add meaning, and the structural and logical implications of the hierarchy and relationships allow inferences to be drawn. If an object is in a subclass of the class of red objects, the inference engine will conclude correctly that the object is red.

When the possible values of an attribute can be enumerated, the attributes are called facets and the classification scheme a FacetedClassification.

An ontological structure lacking hierarchy is a SemanticNetwork. Another is a TopicMap, where concepts are connected without specifying the relationship (discoverable from the contents).

In Philosophy, there is an implied commitment to the existence of the concepts. In ArtificialIntelligence, the concepts need to be "formal," that is machine readable. In Linguistics, "shared" emphasizes the consensual nature of concepts (as words in some human language), merely conventions of the CommunityOfDiscourse?.

ResourceDescriptionFramework (RDF) allows descriptions of resources to be communicated between humans and their agents, application programs.

The WebOntologyLanguage (OWL) extends RDF with more controlled vocabulary for describing properties and classes. Examples are equality, cardinality, symmetry, friend-of, enumeration.

The SemanticWeb is an Ontology (or a web of interdependent ontologies) that uses WebOntologyLanguage to define all resources identified by a URI by means of statements about their relations to other resources.

Ontologies are being developed as specific concept models by the KnowledgeManagement community. They can represent complex relationships between objects, and include the rules and axioms missing from a SemanticNetwork. Ontologies that describe knowledge in a specific area are often connected with systems for DataMining? and KnowledgeManagement."


Ontologies resemble faceted taxonomies but use richer semantic relationships among terms and attributes, as well as strict rules about how to specify terms and relationships. Because ontologies do more than just control a vocabulary, they are thought of as knowledge representation. The oft-quoted definition of ontology is "the specification of one's conceptualization of a knowledge domain."

Ontologies, because they are machine-readable, aim to move the complexity of the system into how the information is organized rather then the application that processes that information. This way, the application can be standardized while the domain-specific information can be customized over time.


An ontology is a formal, explicit specification of a shared conceptualization". "Conceptualization" refers to an abstract model of phenomena in the world by having identified the relevant concepts of those phenomena. "Explicit" means that the type of concepts used, and the constraints on their use are explicitly defined. "Formal" refers to the fact that the ontology should be machine readable. "Shared" reflects that ontology should capture consensual knowledge accepted by the communities.

Dieter Fensel

In computer science, an ontology is the attempt to formulate an exhaustive and rigorous conceptual schema within a given domain, a typically hierarchical data structure containing all the relevant entities and their relationships and rules (theorems, regulations) within that domain. The computer science usage of the term ontology is derived from the much older usage of the term in philosophy, where it means the study of being or existence as well as the basic categories thereof. See ontology (philosophy).


RT - Categorization, Classification, CommunityOfDiscourse?, ConceptualModel?, ControlledVocabulary, FacetedClassification, MetaData, Polyhierarchy, SemanticNetwork, SemanticWeb, Taxonomy, TopicMap, WebOntologyLanguage (OWL)

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Created by: admin last modification: Wednesday 13 of April, 2005 [17:19:13 UTC] by admin