Re: "Hard" Key Determination Method is Easy. DNF Paper is Done..

From: Derek Asirvadem <derek.asirvadem_at_gmail.com>
Date: Mon, 9 Feb 2015 03:32:37 -0800 (PST)
Message-ID: <694b8c03-9c5e-4dc1-a4f5-c2b14fece057_at_googlegroups.com>

> On Monday, 9 February 2015 21:18:17 UTC+11, Nicola wrote:
> In article <bef08005-8a74-4b97-8fce-652022af0e0c_at_googlegroups.com>,
> Derek Asirvadem <derek.asirvadem_at_gmail.com> wrote:
>
> > Guys and Dolls
>
> This prompts me to point out that Nicola is an Italian *male* name. I
> usually get treated better than I am worth in public forums when I omit
> that :)

Thank you for the correction. I have niece named Nicholla.

> > - No redundancies;
>
> In StudentExamination, the fact that, say, Room 101 will host the
> Networks exam on 3/10, 1pm, is repeated for each student taking that
> exam. This is a form of redundancy.

???

Welcome to the world of Relational Databases, Nicola. I see this is your first foray. There is lots to learn. It would be better if you asked a question about what you do not know, rather than making a declaration.

I have no idea what you mean. There is not enough specific info in that statement for me to make a specific answer. So let me take that step by step. Please answer (at least) yes or no to each part.

1. Are you sure you know what Redundancy means, whose "definition" are you using ? (If you are using Date' or Darwen', I know that they are wrong, because they don't know what a Relational Database is, and they think migrated keys are "redundancies". Other pig poop eaters may well think that same.) 1.a That there are no "forms" of redundancy. Either you have it, or you don't ?
2. Are you saying that there is one row in StudentExamination for (your quoted values): Student Course DateTime Room xxxxxx Networks 3/10, 1pm 101 (Student not given)

Or many rows, one per Student, with those three values, repeated x no of students ?

3.  Are you aware, that there are two (not one) foreign keys in StudentExamination ?
3.a PK of CourseExamination ( DateTime, Room, Course )
3.b PK of StudentEnrolment  ( Student, Course )

4.  Are you aware that [3.a] and [3.b] are migrated foreign keys ?

4.a That there is no choice about it, if integrity PK->>FK is required ? 4.b That ( Student, Course, DateTime, Room ) must be carried

5. Ok, now that you have gone through the questions, on what basis, and what columns exactly [ I understand ( Course, DateTime, Room ) ], is it Redundant ? (I couldn't care less about "forms".)

6. And why exactly is ( Course, DateTime, Room ) included in the "forms of redundancy" list, and ( Student ) excluded ? 6.a Note that Student is "repeated" (by your wording) for every Course they take.

7. And what exactly, would you do, to fix this "form of redundancy" that you claim ? Either in the data model as is, with a correction, or fell free to supply the data model or text DDL of the Record Filing System that you would use. Of course, it too, must not have the "forms of redundancy" that you complain about, either Relational Key columns xor Record IDs.

> > no Update Anomalies
>
> Yes, that may well be the case, with the proper inter-relational
> constraints in place.

I am saying that that is the case with the constraints that are in the model. You don't have to worry about anything that could be, should be, would be, just what is documented.

Either state that you agree, or state that my claim is false, with a reason, not could be would be's.

If you don't know then say nothing, instead of demeaning what you don't know with allegations that cannot be dealt with. That is dishonest.

> For example, the redundancy mentioned above does
> not cause update anomalies by virtue of a referential integrity
> constraint.

Gibberish.

Name the constraint you are talking about. Either one in the model (they are all named) or the one you identify as missing (eg. TableX::TableY)

Start of lesson.

Thank you for looking at the pictures. Use the blue link, and read the IDEF1X Intro document.

Cheers
Derek Received on Mon Feb 09 2015 - 12:32:37 CET