Consider the relation CLASS(Course#, Univ_Section#, InstructorName, Semester, BuildingCode, Room#, TimePeriod, Weekdays, CreditHours). This represents classes taught in a university with unique Univ_Section#. Give what you think should be various candidate keys and write in your own words under what constraints each candidate key would be valid.
What will be an ideal response?
Possible candidate keys include the following (Note: We assume that the values of the
Semester attribute include the year; for example "Spring/94" or "Fall/93" could be values for Semester):
1. {Semester, BuildingCode, Room#, TimePeriod, Weekdays} if the same room cannot be used at the same time by more than one course during a particular semester.
2. {Univ_Section#} if it is unique across all semesters.
3. {InstructorName, Semester} if an instructor can teach at most one course during each semester.
4. If Univ_Section# is not unique, which is the case in many universities, we have to examine the rules that the university uses for section numbering. For example, if the sections of a particular course during a particular semester are numbered 1, 2, 3, …then a candidate key would be {Course#, Univ_Section#, Semester}. If, on the other hand, all sections (of any course) have unique numbers during a particular semester only, then the candidate key would be {Univ_Section#, Semester}.
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