Re: what are keys and surrogates?

On Jan 10, 5:05 pm, "David Cressey" <cresse..._at_verizon.net> wrote:
> "David BL" <davi..._at_iinet.net.au> wrote in message
>
> news:e6ba98c3-bc53-45a6-87c6-ea11e8c88616_at_p69g2000hsa.googlegroups.com...
>
>
>
>
>
> > On Jan 10, 1:22 am, Marshall <marshall.spi..._at_gmail.com> wrote:
> > > On Jan 9, 8:07 am, David BL <davi..._at_iinet.net.au> wrote:
>
> > > > On Jan 9, 1:25 pm, Marshall <marshall.spi..._at_gmail.com> wrote:
>
> > > > > This issue goes away if we relax 1NF and allow attributes that are
> > > > > lists or relations. This gives us nested structures. (Nested
> relations
> > > > > are not particularly controversial around here.)
>
> > > > In addition to my previous post, I wish to add another comment
> > > > regarding my suspicion with RVAs. The tuples of a relation are
> > > > supposed to represent facts, but what does it mean when a relation
> > > > merely represents a value?
>
> > > The question is meaningless. The distinction you are drawing
> > > does not exist.
>
> > In what sense do tuples of an RVA represent propositions in *the* UoD?
>
> > > > Isn't the RM meant to have some close
> > > > association with FOPL?
>
> > > Yes.
>
> > > > It seems to me there is a fundamental difference between
>
> > > > a) a large collection of propositions relevant to a particular UoD;
> > > > and
>
> > > > b) a composite data structure such as an AST which simply
> > > > "is what it is"
>
> > > This is an illusion. There is no difference.
>
> > Hmmm. Unfortunately you didn't respond to my last paragraph which was
> > more tangible.
>
> > I don't believe the distinction is an illusion. I'll have a go at
> > providing an objective measure on a given relational database d...
>
> > Let B(d) equal some measure of the amount of information in d,
> > quantified as the total number of bits required to store all the data
> > (accounting for "compressibility").
>
> Off topic.
>
> I prefer quantified as the difference in entropy between the state that
> includes d and the state that excludes it. I believe that, except for a
> scale factor, the two measure boil down to the same thing, except for one
> subtle difference:
>
> Using entropy as the measure enables one to consider information content as
> being context sensitive. That is, if d is to be included in some other
> database e, then the information provided by d to e is the entropy
> difference between e and e+d (where "+" is suitably defined).

Are you suggesting that when d is included in e, there are less states available for d? Received on Thu Jan 10 2008 - 09:42:38 CET