# Is-a | | In knowledge representation and ontology components, including for object-oriented programming and design, **Is-a** is a subsumptive relationship between abstractions, wherein one class A is a subclass of another class B . In other words, type A is a subtype of type B when A's specification implies B's specification. That is, any object that satisfies A's specification also satisfies B's specification, because B's specification is weaker. | |-|-| | | wikipedia:: [Is-a](https://en.wikipedia.org/wiki/Is-a) |