Re: [xtm-wg] Summary of PM discussion

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

Sam Hunting wrote:

> It's surprising that ER diagrams aren't included ;-).
> 
> Another expressed concern is that the notation proposed
> may bias the data model. For example, UML is by
> definition an OO approach, yet systems that must manage
> topic maps that are terabytes in size may not want the
> overhead of objects.

The use of UML or any other object modeling formalism to define the
processing model does not impose an object implemented implementation in
any way. On the other hand, using E-R diagrams to define relational
structures pretty much does impose a relational view on an
implementation (at best, forcing OO implementors to intuit the
appropriate objects from the tables).

For example, I've gone through the exercise of defining the object model
that reflects the HyTime processing model (currently standardized as the
HyTime semantic grove), but a system that exposes that model through an
API could easily be built as a relational system, which would be a
natural choice for a large-scale system given that the HyTime processing
model *is mostly indexes*.

But I would not in any universe define the API for HyTime as a set of
relational tables.

> 
>     * "UML can avoid using notes by using a constraint
>        language, either the built-in OCL or a scripting
>        language like Python."
> 
> A concern with OCL (Object Constraint Language) is whether
> it understands sets. (Python, of course, could be made to.
> This seems perilously close to an implementation, however.)

The use of Python as a constraint language is just a syntax choice: it
doesn't imply that you would actually *implement* the constraint
checking with Python. It's a just a syntax that we found easy to think
in. Choose any syntax you like. Use EXPRESS' constraint language. But
I'm sure that OCL can express constraints and operations on sets. My
collegue John Heintz can tell us for sure--his previous job was
implemnting a system that validated OCL constraints over UML models.
 
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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