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Re: Constraints and Functional Dependencies

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sat, 24 Feb 2007 23:37:16 +0100
Message-ID: <45e0bdad$0$320$e4fe514c@news.xs4all.nl>


paul c wrote:
> 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?

Yes.

> 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.

I see. I overlooked that. Thanks. Received on Sat Feb 24 2007 - 16:37:16 CST

Original text of this message

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