SAFETY AND TRANSLATION OF COMPLEX VALUE CALCULUS QUERIES

Abstract

The practical integration of user-defined functions in the relational algebra is relatively straightforward. However, it is significantly more difficult to support this in the relationsl calculus. Since most query languages are calculus-based, translation of such queries with functions into the equivelent algabra queries becomes a serious problem. This paperexplores the issue of the semantics of complex value calculus queries in the presence of functions. The class of domain independent queries is known to be undecidable. We identify two large decidable subclasses of domain-independent formulas with external functions, namely, the embedded evaluable and embedded allowed formulas. Wethen define a recursive class of embedded allowed' database programs and prove that embedded allowed stratified programs satisfying certaion constraints are embedded domain-independent. Finally we develop an algorithm for translating embedded allowed queries into equivalent algebraic expressions as a basis for evaluating safe queries in all calculus-based query classes.