Implementation of a Capability-Based Data Abstraction

One important feature in programming language design is an appropriate data definitional facility. Criteria now recognized as important are the concepts of information hiding and data abstraction. The problem, however, is to embed these ideas into languages. Although including these ideas has often led to the design of a new language, that is not always necessary. Such facilities may be added to languages like PL/1 or Pascal. This report discusses the inclusion of such facilities within one such PL/1 compiler. While the resulting system does not have the optimal set of protection features, it does have several advantages: the base language is known to a large class of programmers, there are many such compilers already written, and the system achieves almost as much protection as is needed.