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Re: XML spec and XSD

• From: Rick Jelliffe <rjelliffe@allette.com.au>
• To: xml-dev@lists.xml.org
• Date: Mon, 16 Nov 2009 18:42:49 +1100

Len Bullard wrote:
> That's nuts and the opinion of a designer who writes code wonderfully but
> very few technical documents of any real complexity.
>   
As a subsystem gets more complex, we need addition levels of  'meta' to 
make the complexity tractable.

So we progress from plain documents to documents with namespaces to 
documents with content models and facets to documents with the content 
models and facets organized into types or patterns, and so on.  (The 
current stack of 'meta' currently ends just short of handling versions 
and variants well IMHO.)

So I think there is a requirement for agility: can a developer make an 
XML subsystem with just the right amount of 'meta' for their project?  
To oversimplify their positions:  Tim is keen that the developer who 
needs the least amount of 'meta' can have it (with DTD-less XML); 
Michael is keen on the person who needs quite a lot of meta (with typed 
information); Len is keen on the developer who needs a bit of 'meta' but 
not too much (the industrial document developer).  I guess I am 
concerned with developers who need kinds of 'meta' which cannot be 
productized or packaged well: bespoke 'meta'...

But the agility requirement is that it should be relatively easy to go 
from one level of 'meta' to the next, either up or down, with much less 
than commensurate effort.  I think moving from no-DTD XML to DTD-valid 
XML is that kind of low effort that allows agility. And moving from DTD 
to RELAX NG again is agile. But XSD works against agility: first because 
of its multiplication of concepts, but also because buying into the PSVI 
can represent a fundamental change in how you process and treat the 
data:  in practice, I think it is the choice between having a flow of 
documents (XML infoset), or having a DBMS (typed infoset or PSVI.)  The 
PSVI allows and promotes one system architecture (non-XML infoset) and 
works against others (XML infoset-based flows): so it is not just a 
neutral way of organizing XML data in any architecture, as you would 
want if you prized agility.

Cheers
Rick Jelliffe

• References:
  • RE: XML spec and XSD
    • From: "Len Bullard" <cbullard@hiwaay.net>