Syntactical characterization of a subset of domain-independent formulas
Journal of the ACM (JACM)
A rough set model of information retrieval
Fundamenta Informaticae - Special issue: to the memory of Prof. Helena Rasiowa
The Recursive Unsolvability of the Decision Problem for the Class of Definite Formulas
Journal of the ACM (JACM)
Rough Sets: Theoretical Aspects of Reasoning about Data
Rough Sets: Theoretical Aspects of Reasoning about Data
Principles of Database Systems
Principles of Database Systems
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Answers to queries in terms of abstract objects are defined in the logical framework of first order predicate calculus. A partial algebraic characterisation of the supremum and of the infimum of abstract answers is given in an extended Relational Algebra of the Cylindric Algebra kind. Then, the form of queries is restricted in order to be able to compute answers without the cylindrification operator. For these restricted queries we give a technique to compute an upper bound and a lower bound of abstract answers using only the operators of the standard Relational Algebra.