Re: Modeling question...

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:
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> > > 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!

> 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 - 03:37:33 CET