abstract class:

A class that cannot be directly instantiated (Booch et al. 2005). Compare concrete class.

abstract data type:

A data type that is defined by the operations that manipulate it and thus has its representation details hidden.

abstract interface specification:

A specification that defines the external view of the information hiding class—that is, all the information required by the user of the class.

abstract operation:

An operation that is declared in an abstract class but not implemented.


A computation that executes as a result of a state transition.

active object:

See concurrent object:.


A computation that executes for the duration of a state.


An outside user or related set of users who interact with the system ...

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