Efficient Streaming Algorithms for Tree Matching Problems

With the growing importance of XML in data exchange, much research has been done in providing flexible query mechanisms to extract data from XML documents. In this paper, we focus on the query evaluation in an XML streaming environment, in which data streams arrive continuously and queries have to be evaluated even before all the data of an XML document are available. Two algorithms will be discussed. One is for the unordered tree matching, by which only ancestor-descendant and parent-child relationships are considered. It requires O(|T’|?leafQ) time, where T’ is a subtree of document tree T, in which each node matches at least one node in query Q and leafQ is the number of leaf nodes in Q. The other is for the ordered tree matching, by which the left-to-right order of nodes must also be taken into account. It runs in O(|T’|?|Q|) time. Furthermore, our algorithms achieve high time performance without trading off space requirements. They have the same caching space and buffering space overhead as state-of-the-art stream-querying algorithm. We show the efficiency and effectiveness of our algorithms by a lot of experiments.