Layering and multiple views of data abstraction in Ada: techniques and experiences

Abstract

This paper describes the results of a study to investigate alternative techniques for using private types and packages to limit visibility of declarative items in Ada. Shortfalls of the conventional technique of applying private types, with regard to issues of recompilation, source code integrity.limiting visibility. performance. support of debugging, and interrelating abstractions, are identified.Possibly other developers of large Ada systems have encountered these issues; an analysis of over two million lines of Ada software developled for the Army, Navy, and Air Force shows that private types are rarely used. This paper describes a series of unconventional techniques for using private types and packages to layer more abstract packages on top of less abstract packages, and to develop multiple views of abstract data types applicable to different t:lasses of users. The promising techniques were applied on an actual software engineering problem, the development of a tree-builder component of an Ada-to-DIANA translator.A description of experiences, in which the techniques realized benefits for changing and debugging the software and for improving reliability, is provided.