Database and Expert System App II

It has long been recognized that query rewriting techniques are important tools for query optimization and semantic caching and are at the heart of data integration systems. In particular, the problem of rewriting queries using view definitions has received a lot of attention in these contexts. At the same time, the XPath language has become very popular for processing XML data, and there is much recent progress in semantic XPath optimization problems, such as XPath containment, and, more recently, XPath rewriting using views. In this paper we address the open problems of finding equivalent query rewritings using views for XPath queries and views that include the child, predicate and wildcard features (i.e., they are in XP(/, [], ∗)) under DTD constraints. In the process, we also develop novel containment tests for queries in XP(/,[], ∗) under DTD constraints.