Re: Multiple-Attribute Keys and 1NF

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Fri, 31 Aug 2007 09:30:07 -0300
Message-ID: <46d80982$0$4044$9a566e8b@news.aliant.net>

JOG wrote:
> On Aug 31, 3:13 am, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>

>>[snip]
>>"JOG" <j..._at_cs.nott.ac.uk> wrote in message
>>
>>>Well, I have to contest again - you are no doubt referring to "rule
>>>2:The guaranteed access rule", and that makes no reference to the term
>>>identity (...and that is what you asked me about.) Rule 2 is stating :
>>>"every individual value in the database must be logically addressable
>>>by specifying the name of the table, the name of the column and the
>>>primary key value of the containing row."
>>
>>Pardon me for being a stickler about this.  I got this from dbdebunk:

>
> no worries - stickling is fine.
>
>

>>"Each and every datum (atomic value) is guaranteed to be logically
>>accessible by resorting to a combination of table name, primary key value
>>and column name."

>
> Coupla things - Date and Darwen argue against the idea of atomicity,
> and they also complain about the use of 'primary key'. I also think
> Codds use of the term datum is incorrect. Throughout history data has
> required an attribute-value pair. The word is derived from the latin
> for 'statement of fact', its use in science always requires that the
> value is described. Its common sense really - if we don't know what a
> value means, well its just noise. Imagine the binary value 1000001.
> Ascii(1000001) makes it an A, Number1000001) makes it 65, etc.
>
> Either way, this doesn't matter as long as we know what each other
> mean.
>
>

>>A datum is an /atomic/ value, not an individual value.  Atomic--implying
>>that it cannot be separated into components.
>>
>>So having more than one value for a particular role violates the guaranteed
>>access rule either way you look at it.  If the column names aren't unique,
>>then you can't access a particular datum by a column name.  If a value is a
>>collection of component values, then you can't access a particular datum
>>(component value), but only the collection in which it is contained.

>
> Well I've never suggested multiple values contained in a collection.
> But yes as I said, multiple roles does break the guaranteed access
> rule. My question is now (in the continuuing hunt for the theory
> behind 1NF) is why on earth would that be a problem? I don't see any
> affect on the relational algebra.

You earlier suggested that union would suffice for join. But supposing

{{(Color: green), (Color: yellow), (Type: earth)} ,{(Color: black), (Type: neutral)}}

is valid, then the following is valid too:

{{(Color: green), (Color: yellow), (Color: black) , (Type: earth), (Type: neutral)}}

Which, of course, is a union of two of your propositions.

How does that not affect the algebra? Received on Fri Aug 31 2007 - 07:30:07 CDT