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_at_news.aliant.net>
>
> no worries - stickling is fine.
>
>
>
> 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.
>
>
>
> 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.
Date: Fri, 31 Aug 2007 09:30:07 -0300
Message-ID: <46d80982$0$4044$9a566e8b_at_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 - 14:30:07 CEST