Constraint Equations: Declarative Expression of Constraints With Automatic Enforcement
Matthew Morgenstern · Very Large Data Bases · 1984
Constraint Equations provide a concise declarative language for expressing semantic constraints that require consistency among several relations. Each constraint is independently specified in application based terms and provides a natural extension to the limited semantics captured by typical schemata. Automatic constraint enforcement is accomplished by compilation of the Equations into executable routines, according to the algorithms presented here. A prototype system has shown the viability of this approach. The Equations are more natural and perspicuous than the predicate calculus formulas into which they may be translated. The equivalent of both existential and universal quantifiers are expressible directly in Constraint Equations. Algebraic rules for symbolic manipulation of these Equations allow derivation of new Equations and their logical consequences from existing Equations.