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RE: building an object model of a XML schema

• From: Jeff Lowery <jlowery@s...>
• To: 'Paul Cody Johnston ' <pcj@i...>, Jeff Lowery <jlowery@s...>
• Date: Sun, 15 Jul 2001 12:55:11 -0700

Paul Cody Johnston sayz:
------
Jeff,

Can you elaborate on what you're thinking?  I'm trying to parse though
the ideas in this tread to come to clarity of the issues...
------

It's not you, Paul.

------
Your first email said:

 "Well, darn it, I want a data model (just data, thank you) that I can
 express as a physical model through some tranformation, and as a set
 of objects through another transformation. For the general class of
 data models, I would expect the problem to be hard. For hierarchical
 data models only, I think the problem is much easier, but not
 simple."

Here I am interpreting "physical model" == "a textual (or binary)
syntax"; "general class of data models" == "data which can exist as a
graph rather than just a tree", and "heirarchical data models" ==
"data in the form of a tree only".
-------

Yeah, sure, that's what I meant.

---------
As I understand it, this discussion is specifically talking about type
systems, and the mappings between them.
---------

Not quite. I see two mappings in this particular case.

1) XML -> object instances
2) XML Schema -> class definitions

But the latter case pretty much can cover the other in the case of code
generation.

--------
It sounds like you want a "theory" or "abstract model" that
generalizes the type systems of programming languages AND the type
system expressed by XML Schemas.  
--------

Actually, I want a tool that somebody else writes, who's figured out all the
hard bits I haven't thought of, so I can use it and have the easy life.

---------
You want this from a practical
standpoint in order to be able to author some description of "what
validity means to me and my application" and be able to automatically
generate an XML Schema and an object model (a type system for a
programming language).  Is this correct?

If so, you are essentially proposing a new schema language that would
be compared to the W3C XML Schema, RELAX, and TREX, to name a few.
----------

Oh God!! Not another schema language! Is that what I'm asking for? 

Yeah, I think you're right. Darn it all.

----------
This is true because there is no such thing as a meaningful "abstract
model" without a formal description of that model.  And when you write
a formal description, you've essentially written a language that has a
syntax; i.e. any formal description is essentially a syntax.

Perhaps you could:

(1) Explain the real-world application that led your mind to post
    about this in the first place.  Certainly this stuff boils down to
    need.
----------

Read subsequent posts, they might help.

-----------
(2) Provide an example of what the abstract type model would look
    like, based on the application in (1).
----------

I would want to spend some time on that. My subconscious is churning away on
it but it hasn't "dinged" yet.


-----------
AFAIK, the state of the art in type systems is occurring in the
functional language camp.  If a true general type system exists, those
theories are a good start.  However, it gets pretty technical over
there, you need a strong mathematical background to penetrate their
ways of expressing ideas.
-----------

Well, I supposedly have strong mathematical background, but my old college
textbooks only serve to wistfully remind me of how smart I use to be.
("Where have all the gray cells gone? Long time passing...")


Regards, 

Jeff

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