Extending SQL-92 for OODB access: design and implementation experience

This paper describes the design and implementation of a query engine that provides extended SQL-based access to the data managed by an object-oriented database system. This query engine allows extended SQL queries to be embedded in C++ programs or issued interactively as from a command line interface. The language supported by the engine is the complete SQL-92 select statement plus object extensions for navigating along paths and embedded structures, querying nested sets, and invoking member functions. In addition, an object-oriented SQL view facility is provided. Using this view facility, one can define object-oriented views; one can also define views that flatten complex OODB schemas, allowing direct access by existing tools designed to provide remote access to relational databases. The view facility also supports the definition of views that include reference and set-valued columns based on other views, thus allowing entire "view schemas" to be created. This paper describes the SQL-92 query and view extensions and discusses a number of issues that arose on the way to the implementation that is currently running on top of the ObjectStore OODB system.