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)
Cyclic covers are shown to characterise disjunctive stable models of unstrati-fied deductive databases, and to facilitate top-down query processing, query compilation and view updating under the disjunctive stable model semantics. Such processing is shown to be more complex than comparable processing of stratified databases.
A method is presented for computing minimal answers of the form A in disjunctive deductive databases under the disjunctive stable model semantics. Such answers are constructed by repeatedly extending partial answers. Our method is complete (in that every minimal answer can be computed) and does not admit redundancy (in the sense that every partial answer… (More)