Abstract
A database management system designed for instructional use should offer facilities usually not required in a commercial environment. One of the most important features desirable in such a system is its ability to perform query transformation. The use of an universal symbol and tree manipulation system to perform query translation, decomposition and optimization is described in the paper. Examples of transformation rules required to translate SQL expressions into equivalent QUEL expressions, decompose SQL expressions into parse trees and perform optimization of expressions based on relational algebra are shown. An experimental relational DBMS using the above approach is currently under development at the University of Houston. It supports various nonprocedural query languages within a single system, using a unified database dictionary. Cross-translation between various query languages is allowed. The results of every important phase of the query transformation during its execution are interactively available to the system user.
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