Many papers have been written on extensible query optimizers. 1 Most extensible query optimizers attempt to break the optimization problem into two pieces. These two components are called the model and the search engine. The search engine defines the interfaces between the search engine and the model, and provides the code to expand the search space and to search for the optimal plan. But few specifically focus on the model .
Query optimization is introduced in the following section.
Extensible query optimizers are optimizers that allow new features added to a database system to be easily incorporated into the query optimizer. Extensibility is covered in section 4. 1.