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Re: [xml-dev] Caution using XML Schema backward- or forward-compatibilityas a versioning strategy for data exchange

noah_mendelsohn@us.ibm.com wrote:
> Actually, I'm not convinced that's always the reason.  In many cases, the 
> reason you want extensibility is that some core format or business 
> document is to be extensible in different ways by different organization. 
> So, an entire industry might agree on an extensible invoice or purchase 
> order format, with the understanding that individual organizations using 
> the document can add their own additional tracking fields and the like. In 
> such cases, it would be inappropriate to try and route all the private 
> extensions through a central authority, no matter how quick and responsive 
> that authority is. 
Yes, standards organizations like OAGi and UBL fall into this category 
as they are going across verticals, so they include an extension 
mechanism here. But the problem with extension mechanisms in general is 
that it creates on off implementations, and if you are doing B2B 
scenarios and many trading partners with multiple implementations, it 
makes it counter productive.

> One of the important dimensions to consider is that some XML languages 
> are, for good reasons, evolved completely centrally.  Others are evolved 
> by a limited number of organizations, sometimes in cooperation, but 
> sometimes in competition.  It's not at all unusual for one organization to 
> pick up a programming language, document format, etc., to change it, 
> perhaps in compatible ways or perhaps in other ways, and to promote the 
> use of its version(s) in competition with others that are out there.  This 
> certainly happened with HTML for quite awhile.  Finally, as mentioend 
> above, some languages are intended from the start for decentralized 
> enhancement or evolution.  In many cases, those languages prove to be some 
> of the most interesting and powerful for users.

All agreed, but again if we focus on B2B issues, and particular the 
compatiblity issues that existed and still exist with HTML, you have to 
use extensions wisely. Unfortunately, most instances from my experience 
when dealing with Industry specific schemas/grammars is that the reason 
for the one offs is because members have felt that their particular 
requirements couldn't be expressed in the their needed time frame. And 
it's been directly related back to the speed at which their requests are 

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