Abstract
Developers of application software must often work with “legacy systems.” These are systems that have evolved over many years and are considered irreplaceable, either because it is thought that duplicating their function would be too expensive, or because they are trusted by users. Because of their age, such systems are likely to have been implemented in a conventional language with limited use of data abstraction or encapsulation. The lack of abstraction complicates adding new applications to such systems and the lack of encapsulation impedes modifying the system because applications depend on system internals. We describe our experience providing and using an object-oriented interface to a legacy system. © 1989, ACM. All rights reserved.