The CI as described above has no user interface. To be able to control and manage the coordination between the subsystems, the PE control system (PECS) was implemented with some functionalities that enable the user to have some control over the CI.
The PECS is built on top of a simple DBMS and a simple compiler for the update rules and the constraints. The user specifies the constraints and/or the update rules using a certain format (a language), then the compiler transforms this to C code that is integrated with the system for constraint checking, and for applying the update rules. The compiler consists of two parts, a parser and a code generator. In the first phase the complexity of the compiler was reduced by making the user language less sophisticated.