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   Re: Schema concepts

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  • From: "Bill la Forge" <b.laforge@jxml.com>
  • To: <jlowery@scenicsoft.com>, "XML-Dev Mailing list" <xml-dev@xml.org>
  • Date: Sat, 19 Feb 2000 13:05:22 -0500

From: Jeff Lowery <jlowery@scenicsoft.com>
> I've spent most my career writing code mapping relational schemas (and,
> lately, XML-Schemas) to application-specific class structures and let me
> tell ya-- it ain't a lot of fun. 

I couldn't agree more. I've spent two years working on XML/Java mappings.

> Not to mention that if you talk 'database' to most programmers, you tend to
> get glazed looks. 

Mapping code ends up dealing with a lot of meta and meta-meta concepts. Ideas that
may be easy to express in code but hard to put in English, and even harder to 

> So now comes along this new hierarchical data
> structure, called XML, which more easily maps to OOP classes than relational
> tables do. All we need is some schema to enforce data integrity, and all
> this data flying around from app to app has some chance of being correct.

I disagree here. Schema validation can only go so far. Linear thinking drives
us to diminishing returns. I think what we need to complete the validation
is to involve the application logic (or some clearly defined portion of it).

Yes, we want to keep most of the validation logic out of the application. But we
also need some hooks in the mapping process that can supplement schema

> Now, somebody is going to try to make a tool that maps XML-Schemas to class
> definitions of my favorite OOP language of the moment. 

Woops! You started this with mapping schemas to application-specific class
structures. But now it almost sounds like you are talking about compiling
a schema, which a lot of folks are doing. That's a much easier problem, though
I personally don't think it buys you as much.

> Don't get me wrong-- I'm not angry, I'm not hysterical. It's just that I've
> seen a lot of projects fail because they worried too much about being
> optimally efficient or fully featured or technically sexy and not enough
> about simply getting the product out in the simplest way possible. Such, I
> fear, is XML-Schema.

I think there is an approach that will work here. Start small and keep it flexible.
I've already got something, Quick, which seems pretty stable. I've gotten reports
back from a few companies who seem to be happily building product with it.
Yes, I did get one bug report (for which I have a fix).

Admittedly, it only uses a DTD-capable schema. But the schema is just a layer
on top of the engine and is easily enhanced. Quick is Open Source, and I'd be
happy to find a home for it with better support (cvs, FUNCTIONAL mail archive).



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