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Re: Question re: Practical Issues in Database Management

From: TroyK <cs_troyk_at_juno.com>
Date: 21 Mar 2007 09:28:34 -0700
Message-ID: <1174494514.219332.264120@y80g2000hsf.googlegroups.com>


On Mar 20, 5:40 pm, Joe Thurbon <use..._at_thurbon.com> wrote:
> I've been reading some of the books recommended to me recently by c.d.t
> readers, and have a question regarding the Pascal's "Practical Issues in
> DB Management."
>
> My question is: "Have I misunderstood the Pascal definition, or is it
> incomplete/incorrect."
>
> In 5.2.2.2 'Multivalued Dependencies' there are two definitions
>
> Multivalued Dependencies: 'An MVD between two columns exists when sets
> of values in one column are each associated with values in another column'
>
> 4th Normal Form: 'If no multivalued dependencies exist between columns,
> a table is in 4th normal form.'
>
> This definition seems too restrictive. In particular, under those
> definitions, the following tables (AFAICT) would not be in 4th normal
> form. (Although in his book he offers this as an example of 4th normal
> form.)
>
> EMP# Project | EMP# Activity
> ==== ========= | ==== ========
> 1 Services | 1 DEBUG
> 1 Education | 1 SUPPORT
> 2 Services | 2 DEBUG
> 2 TEST
> 2 CODE
>
> From other reading that I've done, the Pascal MVD definition seems a
> little different to the standard ones. e.g.,
>
> http://www.utexas.edu/its/windows/database/datamodeling/rm/rm8.html
>
> has a definition that involves a third column, as do several other sites.
>
> Many thanks,
> Joe

Hi Joe;

There was an error in the book related to the business rules associated with the 4NF example. You may be able to get the updated errata for the book at www.dbdebunk.com.

For this particular example, the business rules (listed on p 137) should read:
- An employee can be assigned to any specified project and all specified activities
- An employee can be assigned to any number of projects and any number of activities
- Projects and activities are independent of each other - A given project or activity can have any number of employees assigned to it

There is also a correction to diagram "A" in figure 5.8 on the next page (which I'll not try to reproduce here).

The section will probably make more sense with the corrections.

HTH,
TroyK Received on Wed Mar 21 2007 - 11:28:34 CDT

Original text of this message

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