A general technique for querying XML documents using a relational databasesystem

There has been recent interest in using relational database systems to stor e and query XML documents. Each of the techniques proposed in this context works by (a) creating tables for the purpose of storing XML documents (also called relational schema generation), (b) storing XML documents by shreddi ng them into rows in the created tables, and (c) converting queries over XM L documents into SQL queries over the created tables. Since relational sche ma generation is a physical database design issue - dependent on factors su ch as the nature of the data, the query workload and availability of schema s - there have been many techniques proposed for this purpose. Currently, e ach relational schema generation technique requires its own query processor to efficiently convert queries over XML documents into SQL queries over th e created tables. In this paper, we present an efficient technique whereby the same query-processor can be used for all such relational schema generat ion techniques. This greatly simplifies the task of relational schema gener ation by eliminating the need to write a special-purpose query processor fo r each new solution to the problem. In addition, our proposed technique ena bles users to query seamlessly across relational data and XML documents, Th is provides users with unified access to both relational and XML data witho ut them having to deal with separate databases.