RE: [gmt-dev] Re: example meta model etc.

["Ghica van Emde Boas" <emdeboas@xxxxxxxxxxxx>]

Hi Yeu Wen,
Thanks for your comments! They certainly make sense.

The main point of discussion is the question whether it always would be
possible to keep the PIM free of implementation artifacts (or alternatively,
have a third, mapping model, to contain implementation specifics).

A practical example, that I really encountered last year, is, that sometimes
there are requirements for column lenghts and column names in a database.
For example, column names could not be longer than 32 (in a respectable
database like Oracle), and this caused duplicates in my mapping. The
requirement was also that the names should stay meaningful, so that it would
not be too hard to look at the database with a standard reporting tool. I
solved this by having tagged values specifying column names if needed, in
the model, but really this is not a good solution, and of course the PIM
becomes cluttered. The position of Jorn seems to be that we will never need
this.

For now, we decided to let the discussion rest, because for the time being,
we will not have these problems. When the time comes, we will look at it
again. I hope you will stay with us in the discussion!

Regards,
Ghica van Emde Boas
Bronstee.com Software & Services b.v.
e-mail: emdeboas@xxxxxxxxxxxx,
tel: +31 23 5474422,
or: +31 6 53368747 (mobile)
fax: +31 23 5473347


> -----Original Message-----
> From: gmt-dev-admin@xxxxxxxxxxx [mailto:gmt-dev-admin@xxxxxxxxxxx]On
> Behalf Of Y e u W e n
> Sent: Monday, May 24, 2004 5:54 PM
> To: gmt-dev@xxxxxxxxxxx
> Subject: [gmt-dev] Re: example meta model etc.
>
>
> Hi Jorn Bettin and Ghica van Emde Boas,
>
> May I offer my 2 cents worth to clear the perceived misunderstandings I
> am beginning to sense in this thread?
>
> At its current infancy stage, the MDA vision might be achieved by two
> rather different interpretations - these two schools of thought have been
> termed ?elaborationist? and ?translationist? (terms that were, I believe,
> originally coined by Stephen Mellor).
>
> In the elaborationist approach, the definition of the application is
> built up gradually as you progress through from PIM to PSM to Code. Once
> the PIM has been created, the tool generates a skeleton or first-cut PSM
> which the developer can then ?elaborate? by adding further information or
> detail. Similarly, the tool generates the final code from the PSM, and
> this may also be elaborated. (Whether elaboration is required at both PSM
> and Code levels depends on the tool and the circumstances.)
>
> In the translationist approach, the PIM is translated directly into the
> final code of the system by code generation. The transformation (or
> translation) of the PIM into the final code is performed by a
> sophisticated code generator, sometimes called a ?Model Compiler?, and
> symbolised by the large arrow. It is driven by Generation Rules that
> describe how the elements of the PIM are to be represented in the final
> code. The PSM is an intermediate stage in the generation and is internal
> to the code generator. It is generally not visible or editable by the
> developer.
>
> Does it make sense?
>
>
>
>
>
>
> Y e u  W e n
>                   \\\|///
>                \\  ^   ^  //
>                 (  @   @  )
> --------------oOOo--(_)--oOOo----------
> "The mere formulation of a problem is far more often essential than its
> solution, which may be merely a matter of mathematical or experimental
> skill. To raise new questions, new possibilities, to regard old problems
> from a new angle requires creative imagination and marks real advances in
> science."
> Albert Einstein (1879-1955) Physicist & Nobel
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