C. A. Johnson

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The view update problem is concerned with indirectly modifying those tuples that satisfy a view (or derived table) by an appropriate update against the corresponding base tables. The notion of a deduction tree is defined and the relationship between such trees and the view update problem for indefinite deductive databases is considered. It is shown that a(More)
The computational complexity of a number of problems relating to minimal models of non-Horn deductive databases is considered. In particular, the problem of determining minimal model membership is shown to be NP-complete for non-recursive propositional databases. The structure of minimal models is also examined using the notion of a cyclic tree, and methods(More)
The relationship between cyclic covers and perfect models of indefinite stratified deductive databases is discussed with respect to query answering, view updates and partial evaluation. The notion of a conjunctive answer to a database query is introduced, and such answers are shown to have a number of advantages over (the more commonly studied) "(More)
We introduce a top down query answering method which can be applied to indeenite deductive databases at the rst order function free level. Our method combines features of resolution and Bibel's connection method. A form of backtracking is included so as to enable the retrieval of multiple answers to queries. We also discuss two ways in which the search(More)