Rewriting XPath queries using materialized XPath views

Let XP(/, //, [ ]) be the fragment of XPath 1.0, consisting of queries that involve only the child and descendant axes, and predicates without disjunction or negation (and no wildcard nodetests); these queries can be represented as tree patterns. We consider the problem of rewriting a query Q using a materialized view V , where Q,V ∈ XP(/, //, [ ]). We present more efficient algorithms for the following: 1). Determine if an equivalent rewriting of Q using V exists; find the smallest such rewriting, when it exists. A previously-known algorithm runs in O(|Q| + |Q||V |) time. For the special case whenQ is known to be minimal, we present anO(|Q||V |) algorithm. 2). Determine if a (nonempty) contained rewriting ofQ using V exists. We present anO(|Q||V |) algorithm, compared to the previous O(|Q||V |) algorithm. We also present a more efficient algorithm for finding a maximal such rewriting, when it exists. Then we extend this result to a subset of XP(/, //, [ ], ∗) that allows restricted occurrences of wildcard nodetests.