The use of abstract data types to simplify program modifications

If a program is structured using abstract data types as the basic unit of modularity, then that program is much easier to extend or modify. This thesis is illustrated by the staged development of a program to compute prime numbers based on the sieve of Eratosthenes. This paper includes an extensive introduction to the concept of abstract data types and can be used as a tutorial survey. It includes discussions on the use of abstract data types in connection with recent approaches to data abstractions, heirarchical structure, and program design. Abstract data types are an extension and modification of the traditional concept of data type. An abstract data type defines not only a data representation for objects of the type but also the set of operations that can be performed on objects of the type. Furthermore, the abstract data type can protect the data representation from direct access by other parts of the program.