Re: [xtm-wg] [XTM-CMS] Is there no data model?

["Chris Angus" <chris.angus@btinternet.com>]

Lars

> | I agree pretty much with the core sentiment of your statement "To
> | me, the data model seemed absolutely crucial, ..."
>
> I'm glad to hear that. It really is my main concern that people share
> that sentiment.

I believe that there are a core of people who do, but I certainly cannot
answer for everyone.

>
> | I think that for 'conceptual model' you should read 'conceptual data
> | model' or 'abstract data model'.
>
> It really is part of my point that that is precisely what I do not
> do.  I've seen the conceptual model and to me it does not look like an
> abstract data model.  It does not seem to give a lot of guidance to
> someone wanting to create, say, a relational database schema for
> storing topic maps.
>

It is intended to be a conceptual or abstract data model in the sense that
it is not intended to be the physical data model to be used for storing a
topic maps, nor should it be. Having said that, if I look at your EXPRESS
model it's form is not so different to what I think that we will produce,
except for better of worse we are using UML rather than EXPRESS-G.

> Nor does there seem to be any plans for proper description of the core
> operations on topic maps, like merging. Kal posted a document on this
> very issue, which was met with deafening silence.

A part of the problem is that we are working to very tight timescales which
makes such plans quite difficult to put in place.  One of the considerations
being taken into account in the development of the model is 'how does this
support topic map merging and how should we describe that process'.

> What I have seen so far I can only describe as a conceptual model.
> What I want is a data model.  The two are not the same.

If by 'data model' you mean 'the model that I will use for physical storage'
then the two are certainly not the same and nor do I think that they should
be.  The model that we produce might well be directly translatable into
EXPRESS and/or into a relational schema, however that would not necessarily
be the best physical implementation.  I believe that the conceptual model
shouold serve two main purposes.  Firstly it should provide a framework that
allows us to more formally define what a topic map is, what it consists of,
how it maps to information resources, etc. and to assist in describing the
concepts to a reader.  Secondly, we should be able to define operation (such
as merging topic maps) in terms of elements of the conceptual model such
that for any physical implementation of the model there should be a mapping
from the elements of conceptual model to elements of the physical/logical
data model that allows the operations to be directly and unambiguously
mapped and verified in that context.

I think that many people involved in data modelling have paid only 'lip
service' to the notions of different forms and levels of data model as laid
out by ANSI/SPARC, etc.  We see conceptual, logical and physical data models
(or whatever other terms one cares to use) that are almost identical.  Much
of my work tends to be with systems where the physical data model bears
little structural resemblance to the logical data models that map to it or
to the business data models that are being handled.  Systems of this nature
have much simpler underlying physical and logical data models and are much
more robust in the face of change.

>
>   <URL: http://www.doctypes.org/xtm/docs/express-model.pdf >
>
> --Lars M.
>
>
>
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