The earlier concepts of "data type" and "data structure" have gradually merged into the single concept of abstract data type (ADT). This merger has occurred as an outgrowth of research in a number of areas related to the structure and meaning of programs, including the design of programming languages, the theory of programming language semantics, the verification of programs, and the theory of data types and structures. In addition there have been a number of attempts to incorporate ideas about ADTs into programming languages, especially in the context of object-oriented programming, either by extending existing languages or by designing new languages.

The basic concept of abstraction is that a data type should be defined only in terms of operations that are valid on objects of its type, not in terms of how the type is implemented on a real computer (for instance, as a...