Updates and views dependencies in semi-structured databases

Abstract

In this paper we study the classical problem of the impact of an update on a view defined over semi-structured data. We adopt the following working hypotheses: (i) the source document is modeled by an unranked, labeled, ordered tree, (ii) a view v is a tree query whose evaluation on the source document provides a desired partial view of the document, (iii) a class of updates C is also given by a tree query selecting the nodes to modify. We then study the following problem: given a view query v and a class of updates C, is it possible to detect if the view v is independent of each update q in C? We show that the problem is in general PSPACE-hard. We propose a sufficient condition evaluable in polynomial time ensuring the independence of a view v with respect to a class of updates C. We then consider the class of linear view queries for which the problem becomes polynomial. Copyright 2008 ACM.