Destabilizers and independence of XML updates

Abstract

Independence analysis is the problem of determining whether an update affects the result of a query, e.g. a constraint or materialized view. We develop a new, modular framework for static independence analysis that decomposes the problem into two orthogonal subproblems: approximating the destabilizer , that is, a finite representation of the set of updates that can change the result of the query, and testing whether the update and destabilizer overlap via an intersection analysis. Focusing on XML queries as the view language and the XQuery Update Facility as the update language, we present a syntactic query rewriting algorithm for translating queries to destabilizers, and show that intersection checking can be reduced to satisfiability problems for which efficient checkers already exist. We present an implementation based on an expressive tree satisfiability checker and a Satisfiability Modulo Order package, and give experiments confirming that the resulting analysis is both fast and effective.