An XML-to-RDB Independent Translating XQuery to SQL

摘要

XML is fast emerging as the dominant standard for representing data in Internet, so there are increasing needs to efficiently query it. One potential path to this goal is using relational database as bottom storage system for XML data by translating XML into relational database. There are many algorithms for mapping XML Schema to relational schema, while translating XQuery to SQL received less attention. Even the few exiting XQuery-to-SQL methods all depend on the XML-To-RDB mapping algorithms. But in the real applications, an independent method is needed because people can't ensure that the two translating steps come from the same industry projects thus conflicts can't be avoided. Aiming at this problem, we propose an XQuery-to-SQL translating method that is independent on any mapping algorithm from XML to RDB. Our main ideas are as follows: We found a four-tiers structure to realize XQuery-to-SQL. The first tier gets input XQuery from user interface and equivalently simplify it to one of forms that is suit for translation to SQL. The second tier defines a virtual general relational schema and translates simplified XQuery to SQL on it. The third tier translates SQL on virtual general relational schema to SQL on real storage relational schema by constructing a view of it. The fourth tier optimize the created SQL by reduce joins and group the result tuple. Our method has several advantages. First, it separates XQuery-to-SQL method from XML-to-RDB algorithm. Second, it improves the XQuery-to-SQL algorithm by optimizing.