Drawing Updates From Derivations

We propose a method for satisfying update requests in deductive databases. The setting is a generalization of the view update problem in relational databases. Updates can be drawn from goals and input clauses in derivations that are rooted at the request. An update may be invalidated by negation or integrity constraints. Thus, it may be necessary to try other updates, drawn from the same or other derivations. We show that an SLDNF tree provides for derivations from which a complete set of possible updates for a delete request can be drawn. SLDNF trees are generally not complete for insert requests; rather, more derivations than there are in an SLDNF tree have to be computed for obtaining completeness of updates, in general. Therefore, we define view update trees and show that a complete set of possible view updates for insert requests can be drawn from them. We specify a literal selection strategy that avoids the construction of redundant derivations.