Exploring legacy systems using types

We show how hypertext-based program understanding tools can achieve new levels of abstraction by using inferred type information for cases where the subject software system is written in a weakly typed language. We propose TypeExplorer, a tool for browsing COBOL legacy systems based on these types. The paper addresses (1) how types, an in-vented abstraction, can be presented meaningfully to soft-ware re-engineers; (2) the implementation techniques used to construct TypeExplorer; and (3) the use of TypeExplorer for understanding legacy systems, at the level of individual statements as well as at the level of the software architecture-- which is illustrated by usingTypeExplorer to browse an industrial COBOL system of 100,000 lines of code.