Reverse data engineering of E-R-designed relational schemas

A novel solution is presented for the data engineer´s inverse mapping problem: to construct from a relational database schema (RDBS) a corresponding entity-relationship diagram (ERD). The inverse mapping is difficult because many ERDs may correspond to one ERDs, or to none if the schema is not well formed, so it is not clear how to define a mapping in this direction. Nonetheless, it would be desirable to choose the most representative ERD whenever possible, so that the benefits of E-R visualization and analysis can be applied to RDBSs, even after their relation schemes have been changed. The authors present a first approach to an experimental solution for this inversion problem, for the case of an RDBS that was originally designed by an ERD-based algorithm, which means that it was once a canonical relational schema (CRS) and subsequently altered. The demonstration system tracks each `atomic change´ in the CRS and determines, by means of its PROLOG-implemented E-R knowledge base, the corresponding changes in the given ERD. The reasonable restrictions that the present system puts on the legal set of possible changes, for example, on deletions, allow it to trace their effects correctly, so that well-formedness of the ERD is preserved