-- Underscorse (like _idnr_) indicates primary keys

-- idnr=national identification number (10 digits)
Students(_idnr_, name, login, program)

Branches(_name_, _program_)

Courses(_code_, name, credits, department)

LimitedCourses(_code_, seats)
    code -> Courses.code

Classifications(_name_)

StudentBranches(_student_, branch, program)
    student -> Students.idnr
    (branch, program) -> Branches.(name, program)

Classified(_course_, _classification_)
    course -> courses.code
    classification -> Classifications.name

MandatoryProgram(_course_, _program_)
    course -> Courses.code

MandatoryBranch(_course_, _branch_, _program_)
    course -> Courses.code
    (branch, program) -> Branches.(name, program)

RecommendedBranch(_course_, _branch_, _program_)
    course -> Courses.code
    (branch, program) -> Branches.(name, program)

Registered(_student_, _course_)
    student -> Students.idnr
    course -> Courses.code

Taken(_student_, _course_, grade)
    student -> Students.idnr
    course -> Courses.code

-- position is either a SERIAL, a TIMESTAMP or the actual position
WaitingList(_student_, _course_, position)
    student -> Students.idnr
    course -> Limitedcourses.code