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Query evaluation in an XML database requires reconstructing XML subtreesrooted at nodes found by an XML query. Since XML subtree reconstruction can beexpensive, one approach to improve query response time is to use reconstructionviews - materialized XML subtrees of an XML document, whose nodes arefrequently accessed by XML queries. For this approach to be efficient, theprincipal requirement is a framework for view selection. In this work, we arethe first to formalize and study the problem of XML reconstruction viewselection. The input is a tree $T$, in which every node $i$ has a size $c_i$and profit $p_i$, and the size limitation $C$. The target is to find a subsetof subtrees rooted at nodes $i_1,\cdots, i_k$ respectively such that$c_{i_1}+\cdots +c_{i_k}\le C$, and $p_{i_1}+\cdots +p_{i_k}$ is maximal.Furthermore, there is no overlap between any two subtrees selected in thesolution. We prove that this problem is NP-hard and present a fullypolynomial-time approximation scheme (FPTAS) as a solution.

XML Reconstruction View Selection in XML Databases: Complexity Analysis and Approximation Scheme