Sets and negation in a logic data base language (LDL1)

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Abstract
In this paper we extend LDL, a Logic Based Database Language, to include finite sets and negation. The new language is called LDL1. We define the notion of a model and show that a negation-free program need not have a model, and that it may have more than one minimal model. We impose syntactic restriction in order to define a deterministic language. These restrictions allow only layered (stratified) programs. We prove that for any program satisfying the syntactic restrictions of layering, there is a minimal model, and that this model can be constructed in a bottom-up fashion. Extensions to the basic grouping mechanism are proposed. We show that these extensions can be translated into equivalent LDL1 programs. Finally, we show how the technique of magic sets can be extended to translate LDL1 programs into equivalent programs which can often be executed more efficiently

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