Re: Constraints and Functional Dependencies

From: paul c <>
Date: Sat, 24 Feb 2007 20:48:02 GMT
Message-ID: <6w1Eh.1113112$1T2.297190_at_pd7urf2no>

mAsterdam wrote:
> paul c wrote:

>> Enrolment { StudentId, CourseId }  KEY { StudentId, CourseId }
>> (note also that a student may take many courses and that a student may 
>> enrol in a course before a teacher is assigned to it)
>> TutorFor { StudentId, StaffId }  KEY { StudentId, StaffId }
>> It's possible to enter a row in TutorFor where StaffID stands for a 
>> teacher who doesn't teach any course the student is enrolled in.  

> If it is a base table, yes. That seems a little strange though,
> by way of example - what would a row mean beyond
> what is already in the other tables?

I assume you mean what does a row in TutorFor mean? If so, it means a student has a particular teacher in some course. Since the schema allows different teachers for the same course, that is the only way for a student to find out who his teacher for a particular course is.

p Received on Sat Feb 24 2007 - 21:48:02 CET

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