Re: Modeling question...

On Oct 29, 2:37 am, David BL <davi..._at_iinet.net.au> wrote:
> On Oct 29, 9:13 am, JOG <j..._at_cs.nott.ac.uk> wrote:
>
>
>
> > On Oct 23, 3:15 pm, David BL <davi..._at_iinet.net.au> wrote:
>
> > > On Oct 23, 9:05 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
>
> > > > On Oct 23, 2:01 pm, Roy Hann <specia..._at_processed.almost.meat> wrote:
>
> > > > > JOG wrote:
> > > > > > Despite a growing literature, current definitions of "semi-structure"
> > > > > > are woefully inadequate.
>
> > > > > A million people can (and evidently will) talk bollocks, but it's still
> > > > > bollocks.
>
> > > > > > The standard denotation is of data that "does
> > > > > > not fit into the relational model".
>
> > > > > That definition is entirely bogus.  The relational model just applies
> > > > > set theory to first order predicate logic.  If you have "data" that
> > > > > doesn't fit into both of these then you better start hiring mystics to
> > > > > look after it for you.
>
> > > > Indeed. And yet hundreds of peer-reviewed papers have been published
> > > > on the topic. I find this incredibly depressing.
>
> > > Ok, I’ll bite…
>
> > > No doubt any data can be made to “fit” into the relational model.
>
> > Let me state first that I don't believe that the relational model is
> > universally applicable (I'm not sure where you think I have stated
> > that).
>
> When I said "universally applicable" I meant (only) with respect to
> the recording of data, where data means "encoded values".
>
> > However, all data can be stated in predicate logic, and all
> > statements of logic can be modelled in the RM. Hence, i consider it
> > absolutely unarguable that there is any data which cannot be
> > structured as a schema of relations. This is my objection to the
> > semistructure literature.
>
> When you say "data" do you always mean "encoded facts"?
>
> > > The more important question is whether it happens /naturally/.
> > > The relational model works really well when there is a UoD on which many
> > > propositions can be made without needing to introduce lots of abstract
> > > identifiers.
>
> > The RM handles facts as naturally as stating them in predicate logic.
> > And why would one ever model things other than facts in predicate
> > logic?
>
> Exactly!

Then may I suggest that your argument is not with the RM, but with the use of predicate logic to model equations, engines, etc. And yet this to me seems trivially true - if I was modelling a human in an art class I'd use clay, not predicate logic.

Of course the resulting piece of clay would be an "encoded value" and thus, by your definition, data.
And then a bag of such pieces of clay.. its a database! And my mantelpiece at home, which I display them on....its a data warehouse!
And of course, when I spring-clean I am become a DBMS!

;) J.

>
> > I think there is confusion (in general, not simply here!) about what a
> > database is intended to model.
>
> Agreed.
>
> > It models data as it has been stated in
> > the real world, not the things which that data refers to.
>
> Yes that fits with your assumption that data = encoded facts.
>
> However it doesn't make sense when you say data = encoded values.
> Encoded values just "are".  They don't necessarily refer to anything
> in the real world.
>
> > > That’s very common, but it’s not always the case. It
> > > seems to me the question of whether the RM is generally appropriate
> > > for heavily nested composite values is unresolved.   Much of the
> > > world’s data is in this latter form.  Eg abstract syntax trees, rich
> > > text documents, scene graphs.
>
> > > If the relational model is universally applicable, why don’t
> > > programmers enter their programs as relations?   Do you really think
> > > it’s only because of the tools currently available?
>
> > Nope. I think data that requires a high number of predicates compared
> > to the number of statements it models can be cumbersome to manipulate
> > in the RM. Equally I think it misses a trick when it comes to facts
> > that might be represented using logical quantification. However, I do
> > believe this situation can be improved (specifically via greater
> > flexibility in defining predicates and integration of existential
> > quantifiers) and its general declarative principles will be
> > increasingly incorporated into programming languages.
Received on Wed Oct 29 2008 - 12:39:55 CET