A course structure is provided for each course. The course structure specifies the completion requirements for a particular version of a course. Changes in course completion requirements 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.