We show how hypertext-based program understanding tools eve 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 invented abstraction, can be presented meaningfully to software 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 using TYPEEXPLORER to browse an industrial COBOL system of 100,000 lines of code. 1998 ACM Computing Classification System: D.2.2, D.2.3, D.2.7., D.3.4, F.3.1, I.2.2. Keywords and Phrases: Software maintenance, program understanding, program analysis, type inference, documentation generation, variable usage, hypertext. Note: To appear in...