Re: Multiple-Attribute Keys and 1NF

On Aug 31, 3:01 pm, Bob Badour <bbad..._at_pei.sympatico.ca> wrote:
> JOG wrote:
> > On Aug 31, 2:28 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
>
> >>"JOG" <j..._at_cs.nott.ac.uk> wrote in message
>
> >>news:1188556656.192653.305160_at_r23g2000prd.googlegroups.com...
>
> >>>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.
>
> >>How do you deal with join:
>
> > Just wanna emphasize the point that I'm not trying to sell anything
> > here! I'm just exploring the idea (outloud).
>
> >>R {{A:4,A:5},{A:5},{A:5,A:6}}
>
> >>Wouldn't R JOIN R =
> >>{{A:4,A:5},{A:5},{A:5,A:6}, {A:4,A:5,A:6}}?
>
> > Yup I guess a natural join would work exactly like that. Unless you of
> > course you used RENAME so:
> > (R AS r1) JOIN (R AS r2) = {not got the energy to enumerate the 9
> > propositions, entailing 30 pairs}
> > However I'd imagine that before joins one would often be UNGROUPing
> > first.
>
> I disagree. If one uses an RVA to describe the Green+Yellow wire, one
> will want to use the entire relation value in join comparisons.

Hadn't got on to join comparisons yet myself (just been considering cross joins) but I imagine this is a valid point. Is it fair to say that a join comparison can consistently be considered as a cross join followed by a restrict? Received on Fri Aug 31 2007 - 16:38:21 CEST