Students, admins, teachers, and classes

["Alexey Parshin" <alexeyp@gmail.com>]

I'm trying to implement the class and its relations to UMOs. 

It looks like the idea to have three fixed groups (students, admins, teachers) is the only one that works in most situations.

The idea to have flags (is_admin,is_teacher) seemed attractive but: we still need to have several groups. The reasons: marking a person within a group allows us to define, for instance, his admins rights to control the group. But it doesn't change or define any of his rights over UMOs within the course. We can only have it on the group level.

This means, that we still need several groups for every class. Now, the number of these groups can be fixed (that simplifies the code) or variable (I still need to understand - what sense does it make). 
In case of three-group schema, the helper functions may use the group type (to-be-added to the group_list), STUDENTS/ADMINS/TEACHERS (from the to-be-created group_type table), to return person's right within the class:

class_is_student(class_id,person_id)
class_is_admin(class_id,person_id)
class_is_teacher(class_id,person_id)

These functions may be used to validate some user actions.. 

-- 
Alexey Parshin,
http://www.sptk.net