Re: [xtm-wg] A challenge on "the graph"

["W. Eliot Kimber" <eliot@isogen.com>]

Lars Marius Garshol wrote:

> Yes. This is precisely what I think as well.
> 
> | This can't be UML as this model cannot rely on notes.
> 
> This I am far less sure of. UML is sufficiently formal, I think. My
> main concerns with UML are:
> 
>  - it's not all that well known, though better than groves, and it's
>    not too easy to find introductions to it on the net

I'm not sure how you can claim that UML is not that well known--it's the
closest thing to a standard in industry that I've seen. Every copy of
Microsoft Dev Studio comes with a stripped-down version of Rational
Rose. I suppose that most implementors may be more familiar with
traditional relational E-R diagrams than UML, but nothing I've seen has
*more* acceptance than UML. There are certainly good introductions on
the net both at the OMG site and, for example, at the ObjectDomain.com
site.

Besides, the parts of UML that are needed for this exercise can be
explained in about 10 minutes and can be understood by anyone competent
to understand topic maps in general.
 
>  - it is very closely tied to implementation. In fact, UML is more
>    suitable as documentation of implementations and designs than as
>    anything else.

This is not true--UML has been *used* primarily to document
implementations, but there is nothing about UML that *requires* that
use. We use UML almost exclusively to define high-level data models that
are explicitly not implementation models. We also use it to document
APIs. But it's primary value to us is an abstract modeling syntax
(coupled with the formal principals of the Catalysis modeling
methodology, which stresses formal statements of constraint and explicit
bindings across levels of abstraction).

But one nice thing about UML is that the same notation can serve from
the highest levels of abstraction to the lowest levels of implementation
detail, providing a common design and documentation framework for all
aspects of a system (including any XML DTDs, as our paper at last year's
Extreme Markup demonstrated).

I would suggest that a grove property set is necessarily much closer to
implementation than a UML data model need be because it is documenting a
particular data representation approach, not an abstract data model.
 
> Question: does UML now have a concept of set properties? That is,
> properties whose values are sets of objects or primitive values?  

Yes. For any multi-valued property you can further characterize that
value as a set.

  This
> is needed all over for modelling topic maps, and is one of the things
> that attracts me to EXPRESS. That, its formality and precision, and
> the _very_ good standardized graphical representation of EXPRESS.

The main problem with using EXPRESS in this domain is that it lacks the
ability to express some essential types of relationships and properties.
For example, it has no defined way to represent aggregation or
containment *and* no extension mechanism by which to add that semantic
to it. In UML, you can use "stereotypes" to refine the modeling
semantics of any graphical component. EXPRESS has no such mechanism,
which in my mind makes it useless as a general-purpose modeling tool.
EXPRESS, like groves and property sets, was designed to satisify a very
specific, very narrow set of requirements, which it does well, but was
not designed with an eye toward generic extensibility.

I would agree that, graphically, EXPRESS and UML are essentially
equivalent (modulo UML's inherent extensibility through stereotypes).

I would also agree that EXPRESS' constraint language is very attractive
and was one of the things that originally motivated my EXPRESS and SGML
harmonization work--the ability to apply mathematical constraints to
grove definitions, something that the property set mechanism does not
provide (although it provides a place to put such constraints).  Of
course, one could use the EXPRESS constraint language with UML
diagrams....
 
Cheers,

E.

-- 
. . . . . . . . . . . . . . . . . . . . . . . .

W. Eliot Kimber | Lead Brain

1016 La Posada Dr. | Suite 240 | Austin TX  78752
    T 512.656.4139 |  F 512.419.1860 | eliot@isogen.com

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