Using tool abstraction to compose systems

The tool abstraction paradigm, which supports the evolution of large-scale software systems by easing design changes in the system functions, is discussed. Systems that support tool abstraction are structured as a pool of abstract data structures shared by a collection of cooperating ´toolies´, where each toolie provides a piece of the overall system function. When one toolie updates the shared data, other toolies must be notified: otherwise, cooperating-but-independent toolies may not execute, and the overall system function may be compromised. The KWIC (key word in context) index production system is used to illustrate the idea of tool abstraction. The relationship of tool abstraction to other concepts is examined.<>