Improved Bottom-Up Query Evaluation in Positive Disjunctive Databases

It is known that bottom-up query evaluation can be extended to work with disjunctive facts, but there seems to be the common assumption that it is much too ineecient for practical applications. In this paper, we improve the extended bottom-up evaluation by making the resolvable literal in a disjunctive fact unique. In many cases, this reduces an exponential behaviour to a polynomial one. We apply this idea in a Horn-clause bottom-up metainterpreter for positive disjunctive rules and also sketch further possible improvements. This should make bottom-up query evaluation for disjunctive databases practically possible.