In knowledge representation and object-oriented programming and design, is-a is a relationship where one class D is a subclass of another class B (and so B is a superclass of D). In other words, "D is a B" usually means that concept D is a specialization of concept B, and concept B is a generalization 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.

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  • In knowledge representation and object-oriented programming and design, is-a is a relationship where one class D is a subclass of another class B (and so B is a superclass of D). In other words, "D is a B" usually means that concept D is a specialization of concept B, and concept B is a generalization 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 the is-a relationship arises in the context of inheritance 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 relationship, which constitutes the holonym-meronym hierarchy. It may also be contrasted with the instance-of relation: see type-token distinction. When designing a model of the real-world relationship between an object and its subordinate, a common error is confusing the relations has-a and is-a.
  • 知識表現、オブジェクト指向プログラミング、オブジェクト指向設計では、Is-aとは、あるクラスBはもう一つのクラスAのサブクラスであるという関係である。 言い換えれば、"BはAである"は通常、概念Bは概念Aの特化であり、概念Aは概念Bの汎化であることを意味する。例として、「フルーツ」は「リンゴ」、「オレンジ」、「マンゴー」などの汎化である。リンゴはフルーツである(is-a) (Apple is a fruit. )と言える。 オブジェクト指向プログラミングではIs-a関係は継承という概念の中で使われる。たとえばリンゴは、「果肉に種が入った植物」に属するというような、フルーツすべてに共通するプロパティをすべて継承するといって差し支えない。 Is-a関係とは、異なる種類の階層の性質をもつ関係にHas-aがある。 オブジェクトと従属するオブジェクトの論理関係がIs-aか、それともHas-aなのか、いつもはっきりと決定できるものではない。この曖昧さが、Is-aのようなメタ言語的な用語を生み出した。
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  • In knowledge representation and object-oriented programming and design, is-a is a relationship where one class D is a subclass of another class B (and so B is a superclass of D). In other words, "D is a B" usually means that concept D is a specialization of concept B, and concept B is a generalization 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.
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  • Is-a
  • Is-a
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