(ADT) A kind of {data abstraction} where a type's internal form is hidden behind a set of {access functions}.  Values of the type are created and inspected only by calls to the access functions.  This allows the implementation of the type to be changed without requiring any changes outside the {module} in which it is defined. {Objects} and ADTs are both forms of data abstraction, but objects are not ADTs.  Objects use procedural abstraction (methods), not type abstraction. A classic example of an ADT is a {stack} data type for which functions might be provided to create an empty stack, to {push} values onto a stack and to {pop} values from a stack. {Reynolds paper (http://www.cis.upenn.edu/~gunter/publications/documents/taoop94.html)}. {Cook paper "OOP vs ADTs" (http://www.wcook.org/papers/OOPvsADT/CookOOPvsADT90.pdf)}. (2003-07-03)