In
knowledge representation
Knowledge representation and reasoning (KRR, KR&R, KR²) is the field of artificial intelligence (AI) dedicated to representing information about the world in a form that a computer system can use to solve complex tasks such as diagnosing a medic ...
, a class is a collection of individuals or objects.
A class can be defined either by
extension (specifying members), or by
intension
In any of several fields of study that treat the use of signs — for example, in linguistics, logic, mathematics, semantics, semiotics, and philosophy of language — an intension is any property or quality connoted by a word, phrase, or ano ...
(specifying conditions), using what is called in some ontology languages like
OWL. According to the
Type–token distinction, the ontology is divided into individuals, who are real worlds objects, or events, and types, or classes, who are sets of real world objects. Class expressions or definitions gives the properties that the individuals must fulfill to be members of the class. Individuals that fulfill the property are called
Instances.
Relationships
Instantiation
The instantiation
relationship
Relationship most often refers to:
* Family relations and relatives: consanguinity
* Interpersonal relationship, a strong, deep, or close association or acquaintance between two or more people
* Correlation and dependence, relationships in mathem ...
is a relation between objects and classes. We say that an object O, say ''Harry the eagle'' is an instance of a class, say ''Eagle''. ''Harry the eagle'' has all the properties that we can attribute to an eagle, for example his parents were eagles, he is a bird, he is a meat eater and so on. It is a special kind of
is a
In knowledge representation, object-oriented programming and Object-oriented design, design (see object-oriented program architecture), is-a (is_a or is a) is a wikt:subsume, subsumption relationship between abstractions (e.g. type (disambiguation) ...
relationship. Its noted
Concept assertion (
) in
Description logics, a family of logic based on classes, class assertion
Subsumption
Classes can
subsume each other. We say usually that if
A and
B are classes, and all
A instances are also
B instances, then B subsumes A, or A is a subclass of B, for example in the OWL Language it is called 'subclassof'.
[
]
References
See also
* Metaclass (Semantic Web)
In the Semantic Web and in knowledge representation, a metaclass is a class whose instances are themselves classes. Similar to their role in programming languages, metaclasses in Semantic Web languages can have properties otherwise applicable on ...
* Ontology
In metaphysics, ontology is the philosophical study of being, as well as related concepts such as existence, becoming, and reality.
Ontology addresses questions like how entities are grouped into categories and which of these entities ...
* Ontology components
* Description logic
* Type-token distinction
Knowledge representation
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