An interactive design tool for designing CODASYL databases is described. The system is composed of three main modules: a user interface, a transaction analyzer, and a core module. The user interface allows a designer to enter interactively information concerning a database design which is to be evaluated. The transaction analyzer allows the designer to specify the processing requirements in terms of typical logical transactions to be executed against the database and translates these logical transaction into physical transaction which access and manipulate the physical databases. The core module is the implementation of a set of analytical models and cost formulas developed for the manipulation of indexed sequential and hash-based files and CODASYL sets. These models and formulas account for the situation in which occurrences of multiple record types are stored in the same area. Also presented are the results of a series of experiments in which key design parameters are varied. The system is implemented in UCSD Pascal running on IBM PCs.>