Re: teaching relational basics to people, questions

From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 28 Nov 2009 15:47:32 GMT
Message-ID: <oCbQm.55478$PH1.3123_at_edtnps82>



Mr. Scott wrote:
...
> An example might help. In the typical table,
>
> CTRS {COURSE, TEACHER, ROOM, STUDENT},
>
> each row states that a particular COURSE is taught by a particular TEACHER
> in a particular ROOM to a particular STUDENT.
>
> Now, while it can be argued that there can't be a course without a teacher,
> or that there can't be a course without a student, or that there can't be a
> student without a teacher, the room exists independent of whether there is a
> course, or a teacher or a student. ...

That's a good example of mysticism. Unless an application requirement is given that rooms are independent in this way, one might just as easily conclude that CTRS is the only base relation in the db. In that case, the set of rooms must be a projection of CTRS. Without further information, I'd have no choice but to conclude that second choice. In my experience, the implementation of unstated requirements has been a huge unnecessary cost in many db's. Received on Sat Nov 28 2009 - 09:47:32 CST

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