Ontology


Ontology
An ontology is a representation of a set of concepts within a domain and the
relationships between those concepts. It is used to reason about the properties of that
domain, and may be used to define the domain.
Ontologies are used in artificial intelligence, the Semantic Web, software
engineering, biomedical informatics, library science, and information architecture as
a form of knowledge representation about the world or some part of it.
Common components of ontologies include:

• Individuals: instances or objects (the basic or "ground level" objects)
• Classes: sets, collections, concepts or types of objects
• Attributes: properties, features, characteristics, or parameters that objects (and
classes) can have
• Relations: ways that classes and objects can be related to one another
• Function terms: complex structures formed from certain relations that can be used in
place of an individual term in a statement
• Restrictions: formally stated descriptions of what must be true in order for some
assertion to be accepted as input
• Rules: statements in the form of an if-then (antecedent-consequent) sentence that
describe the logical inferences that can be drawn from an assertion in a particular
form
• Axioms: assertions (including rules) in a logical form that together comprise the
overall theory that the ontology describes in its domain of application.
• Events: the changing of attributes or relations

Ontology Language
• An ontology language is a formal language used to encode the ontology. There are a
number of such languages for ontologies, both proprietary and standards-based:
• OWL is a language for making ontological statements. OWL is intended to be used
over the World Wide Web, and all its elements (classes, properties and individuals)
are defined as RDF resources, and identified by URIs.
• KIF is a syntax for first-order logic.
• Rule Interchange Format (RIF) and F-Logic combine ontologies and rules.
• The Gellish language includes rules for its own extension and thus integrates an
ontology with an ontology language.


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