Multiple representations of abstract data types

The concept of abstract data types allows the use of complex objects without concern about their implementation. This is accomplished by the separation of specification from implementation details. Modern programming languages incorporate this concept into their design to attempt to provide adequate facilities for the separation of specification from implementations. For example, Ada allows specification (eg. package specification) and implementation (eg. package body) to be separate library units. The implementation bundles together a storage representation and the operations of the abstract data type (ADT). The specification can be viewed as an ADT which defines an object and a set of operations on it. There is usually a one-to-one correspondence between the specification and implementation. The user of an ADT has no influence on the representation chosen for the ADT. In certain applications it is useful to choose the representation and algorithms. This paper presents the idea of providing such a facility in the context of abstract data types. The separation of specification from implementation must also be preserved