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   Re: [xml-dev] XML Object Serialization

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** Reply to message from tblanchard@mac.com on Wed, 30 Oct 2002 01:31:49 +0100

> On Tuesday, October 29, 2002, at 07:43  PM, Anthony B. Coates wrote:
> > The problem is if the auto-generated XML->Java code is called
> > from all throughout the application codebase.  If the XML changes, 
> > everything breaks.  You need to hide the auto-generated code
> > behind a facade so that almost all of the application code is
> > unable to call it directly.  Then, when there are changes to the
> > XML, the effect on the codebase is limited to a small,
> > pre-determined set of classes.
> Of course, this is only a problem with statically typed languages like 
> Java.  Dynamically typed languages cope much better.

Actually, I don't buy the idea that dynamically typed languages are a
significant help here.  I can write robust code in Java/C++/C#/etc. that doesn't
use any schema validation at all, just application validation.  I can write that
code so that if new elements are added they are ignored.  I can write that code
so that if old elements that I don't need are removed, the application doesn't
care and just keeps on writing.  Etc., etc.

However, it is *expensive* to write such robust code, and in the current
economic climate, difficult to justify.  I'm not convinced that it is so much
cheaper to write robust, defensive code in a dynamically typed language, since
the cost of writing that is the primary issue in my experience, not the
language.  That is why I tend to concentrate my thoughts on how to get the most
value out of schema validation engines without producing unsupportably brittle
code as a side effect.

That said, I am happy to be educated about what can be done with dynamically
typed languages if there is some amazing trick I'm simply missing here.

Anthony B. Coates, Information & Software Architect
MDDL Editor (Market Data Definition Language)


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