Re: Question re: Practical Issues in Database Management
From: paul c <toledobythesea_at_oohay.ac>
Date: Sat, 24 Mar 2007 16:55:40 GMT
Message-ID: <gKcNh.62108$DN.8771_at_pd7urf2no>
>> I've been reading some of the books recommended to me recently by
>> c.d.t readers, and have a question regarding the Pascal's "Practical
>> Issues in DB Management."
>>
>> My question is: "Have I misunderstood the Pascal definition, or is it
>> incomplete/incorrect."
>>
>> In 5.2.2.2 'Multivalued Dependencies' there are two definitions
>>
>> Multivalued Dependencies: 'An MVD between two columns exists when sets
>> of values in one column are each associated with values in another
>> column'
>>
>> 4th Normal Form: 'If no multivalued dependencies exist between
>> columns, a table is in 4th normal form.'
>>
>> This definition seems too restrictive. In particular, under those
>> definitions, the following tables (AFAICT) would not be in 4th normal
>> form. (Although in his book he offers this as an example of 4th normal
>> form.)
>>
>> EMP# Project | EMP# Activity
>> ==== ========= | ==== ========
>> 1 Services | 1 DEBUG
>> 1 Education | 1 SUPPORT
>> 2 Services | 2 DEBUG
>> 2 TEST
>> 2 CODE
>>
>>
>> From other reading that I've done, the Pascal MVD definition seems a
>> little different to the standard ones. e.g.,
>>
>> http://www.utexas.edu/its/windows/database/datamodeling/rm/rm8.html
>>
>> has a definition that involves a third column, as do several other sites.
>>
>> Many thanks,
>> Joe
Date: Sat, 24 Mar 2007 16:55:40 GMT
Message-ID: <gKcNh.62108$DN.8771_at_pd7urf2no>
paul c wrote:
> Joe Thurbon 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
> > > > Joe, I'm guessing that Fabian P meant to say something like "If no > trivial multivalued dependencies exist ...".
Oops, meant to say "If no non-trivial mvd's exist ...".
p Received on Sat Mar 24 2007 - 17:55:40 CET