This project is to design a system for specifying prerequisites and write a software tool for interpreting prerequisites to check for valid enrolments. The project will involve first understanding the current ways in which prerequisites are encoded: random string; interpreted in callista and caidi done by hand; student services manually overrides some rules; calista everything in great detail; caidi designed for reading eg "12 points of programming". The enrollment system, callista, typically lists every single case and is designed for checking when students enrol in a unit. The main deliverable of the project will be a prototype system for defining ad checking unit prerequisite rules. The system should include guidance on how to specify prerequisites, it should facilitate clear specification and checking of prerequisites, and it should enable automatic checking of student enrolments.