[sc34wg3] SIDP vs Assertion types

[Jan Algermissen]

Robert Barta wrote:
> 
> On Tue, Apr 22, 2003 at 06:23:29PM +0200, Jan Algermissen wrote:
> > Yes. This is a basic design decision to be made by TMAs: Is a relationship to
> > be modeled as an assertion or as a property.
> ...
> > > The two extremes being one where I
> > > do everything as SIDPs/OPs and the other where I do everything with
> > > assertion types.
> >
> > Exactly. If you do everything as properties you'd end up with something
> > like a relational schema that only has relations (tables) that represent
> > entity classes and no relations (tables) that represent relationship classes.
> 
> Jan,
> 
> This explanation was very helpful to me, thx!
> 
> So, is it a fair statement to say that TMM is meant as a platform
> ("bus") to integrate data repositories (relational DBs, XMLlish data,
> other TMish data) into ONE common data framework?

In a sense...yes.
> 
> If so, then I would have assumed that the propagators have thoughts
> and/or experiments on this for relational data? 

What exactly do you mean by 'relational data'?


> The HTTPGET
> application is certainly fascinating, but would not fully demonstrate
> the strength of this approach to me. OTOH, you probably would have
> used that already if you had.


I am afraid I don't understand the last sentence, what do you mean?

> 
> Anyway, is this meant for read-only purposes?
> 
>   - application A uses relational DB and a TMA_A describes how to
>     "view" the data TMish
> 
>   - application B models its data as TMA_B and can use data from A
> 
> Or is this also meant in both directions: read and write?

Certainly read and write. If I wrap a relational database with a TM
'frontend' there is of course the possibility to 'add an association'
etc.

> 
> And what about querying? If application B makes a query, is this query
> translated into TM-speak via TMA_B and then propagates to A and is
> executed using the inverse of TMA_A.

Huh?

> 
> Or is my understanding too mechanical and no formalisation of TMA
> definitions can exist? But then how can we formally test TMM
> conformance of an application?

Well, recent postings by Lars on conformance made my realize that it
makes no sense to 'conform to a data model'. Taken to the relational
world, it makes no sense to claim/verify that an application is
conformant to the entity relationship model. Who cares how Oracle et al.
actually implement their stuff? All that counts is that their APIs
(=SQL 'processor') conform to the SQL standard.

So, I really do think that conformance to the SAM (or TMM) makes not much
sense at all, it is entirely a matter o API/Query languge conformance.

What do others think?

Jan

> 
> \rho
> 
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-- 
Jan Algermissen                           http://www.topicmapping.com
Consultant & Programmer	                  http://www.gooseworks.org