Syntactically Recognizable Modularly Stratified Programs

We present an eecient evaluation technique for modularly stratiied 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, preferential vote counting, and matrix diagonalization. Programs written in this style are easier to understand and can be eeciently computed. Another virtue of these programs is that their modular-stratiication properties are independent of the extensional database. We also present compiler optimizations for EMS-programs.