A course structure is provided for each course. The course structure specifys the completion requirements for the particular version of the course. Changes in course completion requirements as they evolve over time are reflected in successive course versions. However, the course requirements that apply to a student are those that applied at the time he or she was admitted to the course, unless a specific transition program has been approved by the faculty. The course structure is shown by listing compulsory components (core components) and/or an options list. The components in both the core and the options list may be subjects or sub-structures, such as majors, sub-majors, choice blocks or streams. Sub-structures themselves have core and option components lists. Details of the subject choices available within each sub-structure may be accessed in the online and CD-ROM versions of the handbook, or by using the complete listing of all sub-structures, sorted by code, which appears in the Study Package Directory section of the print version of the handbook.