We present an efficient evaluation technique for modularly stratified deductive database programs for which the local strata level mappings are known at compile time. We present an important subclass of these programs (called EMS-programs) in which one can easily express problems, such as shortest distance, company ownership, bill of materials, and preferential vote counting. Programs written in this style have an easy-to-understand semantics and can be efficiently computed. Another important virtue of these programs is that their modular-stratification properties are independent of the extensional database.

An overview of the structure of Aditi, a disk-based deductive database system under continuous development at the University of Melbourne, is presented. The aim of the project is to find out what implementation methods and optimization techniques would make deductive databases competitive with current commercial relational databases. The structure of the Aditi prototype is based on a variant of the client-server model. The front end of Aditi interacts with the user exclusively in a logical language that has more expressive power than relational query languages. The back end uses relational technology for efficiency in the management of disk-based data and uses some optimization algorithms especially developed for the bottom-up evaluation of logical queries involving recursion. The system has been functional for almost two years now, and has already proven its worth as a research tool.>