Integration of SQL and XQuery in IBM DB2

Relational database systems have dominated the database industry for a quarter century. However, the advent of the Web has led to requirements for storage of new kinds of information in which the order of information is important and data structure can vary over time and from one document to another. These evolving requirements have given rise to Extensible Markup Language (XML) as a widely accepted data format and to XQuery as an emerging standard language for querying XML data sources. A set of extensions to the Structured Query Language (SQL) called SQL/XML enables XML data to be stored in relational databases, taking advantage of the mature infrastructure of relational systems and combining the advantages of SQL and XQuery. However, building a bridge between SQL and XQuery is challenging due to the many syntactic and semantic differences between the two languages. This paper describes how IBM DB2® deals with this challenge and provides users with a flexible system for storing and processing both relational and XML data.