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517:, that represents how objects combine to form composite objects. For example, if we extended our example ontology to include concepts like Steering Wheel, we would say that a "Steering Wheel is-by-definition-a-part-of-a Ford Explorer" since a steering wheel is always one of the components of a Ford Explorer. If we introduce meronymy relationships to our ontology, the hierarchy that emerges is no longer able to be held in a simple tree-like structure since now members can appear under more than one parent or branch. Instead this new structure that emerges is known as a
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394:(also known as relationships) between objects in an ontology specify how objects are related to other objects. Typically a relation is of a particular type (or class) that specifies in what sense the object is related to the other object in the ontology. For example, in the ontology that contains the concept Ford Explorer and the concept
324:, although they may be independent things. Each attribute can be a class or an individual. The kind of object and the kind of attribute determine the kind of relation between them. A relation between an object and an attribute express a fact that is specific to the object to which it is related. For example, the
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of opinion as to whether numbers and words are classes or individuals). Strictly speaking, an ontology need not include any individuals, but one of the general purposes of an ontology is to provide a means of classifying individuals, even if those individuals are not explicitly part of the ontology.
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Individuals (instances) are the basic, "ground level" components of an ontology. The individuals in an ontology may include concrete objects such as people, animals, tables, automobiles, molecules, and planets, as well as abstract individuals such as numbers and words (although there are differences
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Relation types are sometimes domain-specific and are then used to store specific kinds of facts or to answer particular types of questions. If the definitions of the relation types are included in an ontology, then the ontology defines its own ontology definition language. An example of an ontology
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In formal extensional ontologies, only the utterances of words and numbers are considered individuals – the numbers and names themselves are classes. In a 4D ontology, an individual is identified by its spatio-temporal extent. Examples of formal extensional ontologies are
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As well as the standard is-a-subclass-of and is-by-definition-a-part-of-a relations, ontologies often include additional types of relations that further refine the semantics they model. Ontologies might distinguish between different categories of relation types. For example:
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that together comprise the overall theory that the ontology describes in its domain of application. This definition differs from that of "axioms" in generative grammar and formal logic. In these disciplines, axioms include only statements asserted as
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This tells us that the
Explorer is the model that replaced the Bronco. This example also illustrates that the relation has a direction of expression. The inverse expression expresses the same fact, but with a reverse phrase in natural language.
506:) that clearly depicts how objects relate to one another. In such a structure, each object is the 'child' of a 'parent class' (Some languages restrict the is-a-subclass-of relationship to one parent for all nodes, but many do not).
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relation, and others. The set of used relation types (classes of relations) and their subsumption hierarchy describe the expression power of the language in which the ontology is expressed.
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Ontologies are only true ontologies if concepts are related to other concepts (the concepts do have attributes). If that is not the case, then you would have either a
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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.
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ways in which classes and individuals can be related to one another. Relations can carry attributes that specify the relation further.
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in which they are expressed. Most ontologies describe individuals (instances), classes (concepts), attributes, and relations.
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Ontological
Engineering: with examples from the areas of Knowledge Management, e-Commerce and the Semantic Web. First Edition
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Much of the power of ontologies comes from the ability to describe relations. Together, the set of relations describes the
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aspects, properties, features, characteristics, or parameters that individuals (and classes and relations) can have.
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complex structures formed from certain relations that can be used in place of an individual term in a statement.
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that defines its own relation types and distinguishes between various categories of relation types is the
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Formal
Ontology in Information Systems: Proceedings of the Seventh International Conference (FOIS 2012)
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formally stated descriptions of what must be true in order for some assertion to be accepted as input.
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Software using this ontology could now answer a question like "which cars are made in the U.S.?"
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type relationship which tells us where each car is built. So the Ford
Explorer is
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Asunción Gómez-Pérez; Mariano
Fernandez-Lopez; Oscar Corcho (18 April 2006).
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Description Logics: Foundations for Class-based
Knowledge Representation
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relation types for relations between a single object and a collection
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relation types for relations between an individual and a class
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The addition of the is-a-subclass-of relationships creates a
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For example, in the domain of automobiles, we might need a
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share many structural similarities, regardless of the
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643:. Springer Science & Business Media.
137:Common components of ontologies include:
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509:Another common type of relations is the
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