Tree Reconstruction and Bottom-Up Evaluation of Tree Pattern Queries

An XML tree pattern query, represented as a labeled tree, is essentially a complex selection predicate on both structure and content of an XML. Tree pattern matching has been identified as a core operation in querying XML data. However, almost all the proposed algorithms only deal with unordered trees, by which the order of siblings is not considered. In this paper, we discuss a new algorithm for processing ordered tree pattern queries, for which not only the ancestor-descendant and parent-child relationships, but also the order of siblings are significant. The time complexity of the algorithm is bounded by O(|D|·|Q| + |T|·leaf_Q) and its space overhead is by O(leaf_T·leaf_Q), where T stands for a document tree, Q for a tree pattern query and D is a largest data stream associated with a query node q of Q, which contains the database nodes that match the node predicate at q. leaf_T (leaf_Q) represents the number of the leaf nodes of T (resp. Q). In addition, the algorithm can be adapted to an indexing environment with XB-trees being used. Experiments have been conducted, which shows that the new algorithm is promising.