Journal of Logic Programming, 1(3) 225-240, 1984 Google Scholar Cross Ref Technlcal Report RM-5428-PR, Rand Corp, 1967 Google Scholar Answering Questions by Computer A Logtcal Study. on Threory of Computing, pages 123-134 1980 Google Scholar Digital Library The recurmve unsolvability of the decision problem for the class of defimte formulas. Techmcal Report, ONERA- CERT, 1982 Google Scholar Syntactscal Characteriation of a Subset of Domain Independent Formulas. In 1st lnt'l Conference on Expert Dalabase Systems, pages 271-285, 1986 Google Scholar lntegrity enforcement in deductive databases. North-Holland, Amsterdam, 1968 Google Scholar Our algorithms avoid use of the so-called Dom relation, consisting of all constants appearing in the database or the query.įinally, we describe a restriction under which every domain independent formula is evaluable, and argue that evaluable formulas may be the largest decidable subclass of the domain independent formulas that can be efficiently recognized. We give algorithms to transform an evaluable formula into an equivalent allowed formula, and from there into relational algebra normal form. We introduce relational algebra normal form for formulas from which form the correct translation into relational algebra is trivial. Although both classes have been defined before, we give simplified definitions, present short proofs of their man properties, and describe a method to incorporate equality.Īlthough evaluable queries have sensible answers, it is not straightforward to compute them efficiently or correctly. Subsequent research has focused on identifying large decidable subclasses of domain independent formulas In this paper we investigate the properties of two such classes the evaluable formulas and the allowed formulas. The class of relational calculus queries, or formulas, that have “sensible” answers is called the domain independent class, which is known to be undecidable. Not all queries in relational calculus can be answered “sensibly” once disjunction, negation, and universal quantification are allowed.
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