Accelerating Path-free XML Queries in RDBMS

Abstract

Traditional XML query processing methods, such as XPath and XQuery, are fragile to changes in the underlying XML structure because path expressions cannot accommodate structural variations that may occur in designing or updating XML data. In this paper, we discuss the problem of processing path-free XML queries in a pure RDBMS. It is ideal to list all possible structural variations of a given path-free XML query, though it is non-trivial to devise an efficient implementation due to the combinatorial explosion of potential structural variations. In addition the problems that RDBMS cannot offer an ideal query plan and efficient XML structural join algorithms also pose a big challenge. We teach RDBMS aware of tree structures by adding XML-specific information, and supply FDs among attributes in an amoeba join to eliminate unfavorable results and achieve a marked reduction in the query space. Dealing with XML query in a pure RDBMS efficiently bridges the gap between XML and relational database. Experiments carried out on SQL Server have proven orders of magnitude improvement over the naïve implementation, demonstrating the feasibility of path-free XML query processing using a pure RDBMS kernel.