Query Processing in Embedded Control Programs

An embedded control program can be viewed as a small main-memory database system tailored to suit the needs of a particular application. For performance reasons, the program will usually define low-level data structures to store the database which in turn have to be understood by application developers and maintainers. This is in contrast with the data independence that can be achieved by using a relational database system. However, because of space and performance requirements, the use of a traditional DBMS is not likely to be feasible in this setting. To partly address this, we have developed a query optimizer capable of compiling SQL/OQL queries on a conceptual schema to native Java or C code that navigates lowlevel data structures. Of particular significance is that an arbitrary collection of such structures, perhaps already devised for an earlier version of the control program, can be given as a part of the input. The underlying algorithms used in our optimizer to accomplish this ..