Querying XML data sources in DB2: The XML wrapper

Abstract

The XML Wrapper exploits the federated database capabilities of DB2 to enable SQL applications to query XML data from a variety of sources, including files and web services. The XML Wrapper models hierarchical XML documents as families of virtual relational tables in a federated schema, which can then be queried to extract information from the XML and combine it with from other sources. To keep the wrapper simple and efficient, we take advantage of the existing capabilities of DB2 to the greatest extent possible. Our approach uses the DB2 optimizer's ability to explore the space of join orders and join methods to find good execution plans for queries that include XML documents. We also leverage DB2's view and rewrite mechanisms to allow a simple wrapper to support the full range of SQL queries an application might submit.