Re: what are keys and surrogates?

On Jan 11, 4:28 am, "David Cressey" <cresse...@xxxxxxxxxxx> wrote:
"David BL" <davi...@xxxxxxxxxxxx> wrote in message

news:1d8bc808-c202-45bd-8d04-5ad80bb895ef@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> On Jan 10, 5:05 pm, "David Cressey" <cresse...@xxxxxxxxxxx> wrote:
"David BL" <davi...@xxxxxxxxxxxx> wrote in message

news:e6ba98c3-bc53-45a6-87c6-ea11e8c88616@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx







On Jan 10, 1:22 am, Marshall <marshall.spi...@xxxxxxxxx> wrote:
On Jan 9, 8:07 am, David BL <davi...@xxxxxxxxxxxx> wrote:

On Jan 9, 1:25 pm, Marshall <marshall.spi...@xxxxxxxxx> 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?

No. Did I say something that implies that?

Perhaps not. My understanding is that entropy is defined as a
logarithm on the number of states available to a system, and tends to
be proportional to the number of bits required to represent a
particular state. When two *independent* systems s1,s2 are combined
into a single overall system s = s1 + s2, the total number of states
available to s is the product of the number of states available to s1
and s2, and by property of logarithms, the entropy is additive.

I thought your comment had something to do with coupling between d and
e. ie there being less available states for d in the context of e,
which is why you suggested an entropy measure of information content.

.

Relevant Pages

  • Re: what are keys and surrogates?
    ... regarding my suspicion with RVAs. ... supposed to represent facts, but what does it mean when a relation ... providing an objective measure on a given relational database d... ... Using entropy as the measure enables one to consider information content ...
    (comp.databases.theory)
  • Re: Conservation of Information?
    ... Information entropy is defined ... as binary logarithm. ... another permutations are possible, say abccddeee. ... Its logarithm was proposed by ...
    (sci.physics)