SQL Open Heterogeneous Data Access
Berthold Reinwald (IBM Almaden Research Center)
Hamid Pirahesh (IBM Almaden Research Center)

We describe the open, extensible architecture of SQL for accessing data stored in external data sources not managed by the SQL engine. In this scenario, SQL engines act as middleware servers providing access to external data using SQL DML statements and joining external data with SQL tables in heterogeneous queries. We describe the state-of-the art in object-relational systems and their companion products, and provide an outlook on future directions.