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In knowledge representation

Knowledge representation

Knowledge representation is an area of artificial intelligence research aimed at representing knowledge in symbols to facilitate inferencing from those knowledge elements, creating new elements of knowledge...

, object-oriented programming

Object-oriented programming

Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...

and design, is-a or is_a or is a (subsumption) is a relationship where one class D is a subclass

Subclass

Subclass may refer to:* Subclass , a taxonomic rank intermediate between class and superorder* Subclass , a class that is derived from another class or classes...

of another class B (and so B is a superclass

Superclass

Superclass may be:* The global ruling class created by neoliberal globalization * Superclass , a book about global governance by David Rothkopf, and The Superclass List...

of D).

In other words, "D is a B" (B subsumes D, or D is-subsumed-by B) usually means that concept D is a specialization of concept B, and concept B is a generalization

Generalization

A generalization of a concept is an extension of the concept to less-specific criteria. It is a foundational element of logic and human reasoning. Generalizations posit the existence of a domain or set of elements, as well as one or more common characteristics shared by those elements. As such, it...

of concept D. For instance, a "fruit" is a generalization of "apple", "orange", "mango" and many others. One can say that an apple is a fruit.

In object-oriented programming

Object-oriented programming

Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...

the is-a relationship arises in the context of inheritance

Inheritance (computer science)

In object-oriented programming , inheritance is a way to reuse code of existing objects, establish a subtype from an existing object, or both, depending upon programming language support...

concept. One can say that "apple" may inherit all the properties common to all fruits, such as being a fleshy container for the seed of a plant.

The is-a relationship is contrasted with the has-a
Has-a
In database design and object oriented program architecture, has-a is a relationship where one object "belongs" to another object , and behaves according to the rules of ownership. In simple words, has-a relationship in an object is called a member field of an object...

relationship, which constitutes the holonym-meronym hierarchy. It may also be contrasted with the instance-of relation: see type-token distinction

Type-token distinction

In disciplines such as philosophy and knowledge representation, the type-token distinction is a distinction that separates an abstract concept from the objects which are particular instances of the concept...

.

When designing a model (e.g., a computer program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

) of the real-world relationship between an object and its subordinate, a common error is confusing the relations has-a and is-a.

Is-a

See also