THE SOFTWARE BOOKSHELF

Legacy software systems are typically complex, geriatric, and difficul t to change, having evolved over decades and having passed through man y developers. Nevertheless, these systems are mature, heavily used, an d constitute massive corporate assets. Migrating such systems to moder n platforms is a significant challenge due to the loss of information over time, As a result, we embarked on a research project to design an d implement an environment to support software migration. in particula r we focused on migrating legacy PL/I source code to C++, with an init ial phase of looking at redocumentation strategies. Recent technologie s such as reverse engineering fools and World Wide Web standards now m ake it possible to build tools that greatly simplify the process of re documenting a legacy software system. In this paper we introduce the c oncept of a software bookshelf as a means to capture, organize, and ma nage information about a legacy software system. We distinguish three roles directly involved in the construction, population, and use of su ch a bookshelf: the builder, the librarian, and the patron. From these perspectives, we describe requirements for the bookshelf, as well as a generic architecture and a prototype implementation. We also discuss various parsing and analysis fools that were developed and integrated to assist in the recovery of useful information about a legacy system . In addition, we illustrate how a software bookshelf is populated wit h the information of a given software project and how the bookshelf ca n be used in a program-understanding scenario. Reported results are ba sed on a pilot project that developed a prototype bookshelf for a soft ware system consisting of approximately 300K lines of code written in a PL/I dialect.