OOC:en:1.2 Abstract Data Types

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We call a data type abstract, if we do not reveal its representation to the user. At a theoretical level this requires us to specify the properties of the data type by mathematical axioms involving the possible operations. For example, we can remove an element from a queue only as often as we have added one previously, and we retrieve the elements in the same order in which they were added.

Abstract data types offer great flexibility to the programmer. Since the representation is not part of the definition, we are free to choose whatever is easiest or most efficient to implement. If we manage to distribute the necessary information correctly, use of the data type and our choice of implementation are totally independent.

Abstract data types satisfy the good programming principles of information hiding and divide and conquer. Information such as the representation of data items is given only to the one with a need to know: to the implementer and not to the user. With an abstract data type we cleanly separate the programming tasks of implementation and usage: we are well on our way to decompose a large system into smaller modules.