Recovering structured data types from a legacy data model with overlays

Legacy systems are often written in programming languages that support arbitrary variable overlays. When migrating to modern languages, the data model must adhere to strict structuring rules, such as those associated with an object oriented data model, supporting classes, class attributes and inter-class relationships. In this paper, we deal with the problem of automatically transforming a data model which lacks structure and relies on the explicit layout of variables in memory as defined by programmers. We introduce an abstract syntax and a set of abstract rewrite rules to describe the proposed approach in a language neutral formalism. Then, we instantiate the approach for the proprietary programming language that was used to develop a large legacy system we are migrating to Java.