Towards Integrated Query Processing for Object-Relational and XML Data Sources

The recently increased amount of information stored in XML format has lead to the development and wide deployment of so-called native XML database management systems (XML DBMS). In parallel, (object-)relational DBMS remain well known, approved and widely used for persistent storage of data. There are many research and industrial areas, including virtual enterprises, Web portals, digital libraries, data management systems, etc., where applications need to manage both (object-) relational DBMS and XML DBMS to retrieve information from these kinds of data sources. This has created a need for integrated access to (object-)relational and XML data sources. The focus of our investigation in this context comprises design and development of an integration middleware between the application and the data sources, allowing unified access to the entire information for SQL- and XML-based applications. In this paper, we propose a query processing technique supporting integrated access to (object-)relational and XML data sources via both query languages, SQL and XQuery. The local data sources under integration can be queried from the corresponding unified global views, an SQL-View (for SQL-based applications) as well as an XML-View (for XML-based applications), both offering access to the entire integrated information