# Re: Modeling question...

Date: Thu, 23 Oct 2008 08:15:46 -0700 (PDT)

Message-ID: <de0dc1e9-1953-49d9-ae84-00cab59d1195_at_z6g2000pre.googlegroups.com>

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.
*

No doubt any data can be made to “fit” into the relational model. 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. 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?

What about automated proof systems? Is the knowledge base and data associated with an ongoing proof best represented using a set of relations? I find that quite unlikely. The RA seems to have more to do with set based calculations on known sets of values, rather than symbolic manipulation. Symbolic manipulation involves a lot of recursion and the RA on its own is too weak, which suggests it will take a backseat role. Eg to compute the most general unifier of two given expressions involves recursion in the nested expressions.

I also find it rather telling that relational queries (ie RA expressions) are not themselves represented using relations. Surely if that were useful, many cdt folks would jump at the opportunity to further promote the use of relations. Received on Thu Oct 23 2008 - 17:15:46 CEST