The representation and deductive retrieval of complex objects
Carlo Zaniolo · Very Large Data Bases · 1985
The Relational Data Model and Relational Calculus are extended with Unification and non-recursive Horn Clauses from Logic. The benefits gained include better versatility and a richer functionality for expressing complex Jack, deductive queries and rule-based infer- ences. Applications include semantic data models for Databases, frames for Knowledge-based systems, and Complex Objects for CAD. An Extended Relational Algebra (ERA) is introduced that has the same expres- sive power as the new Calculus. The algorithm given for translating from Calculus to ERA supplies a sound basis for the compilation of these Horn clauses, and their implementation using query optimization and other techniques currently used in database systems.