Re: Versioning of XML Schema and namespaces

Hi,

I thought this made interesting reading in light of what you have been saying. I think what it's saying is that even though versioning is included in the namespace a vocabulary becomes static at that point -

UBL and Object-Oriented XML: Making Type-Aware Systems Work
http://www.idealliance.org/papers/dx_xml03/papers/04-04-04/04-04-04.pdf

I'd be interested to hear some counter arguments, perhaps?

Cheers,

Fraser

Simon.Cox@xxxxxxxx wrote:

Uh oh. There is clearly significant divergence here. 

There appear to be 2 1/2 positions:

1. very formal versioning of namespace identifiers - major.minor
revision number etc - this is in all three of the XML Naming and Design
Rules documents recently published by DON, UN/CEFACT and OASIS
http://xml.coverpages.org/ni2005-01-31-a.html

2. no versioning - eloquently argued by Eliot Kimber in particular, on
both conceptual and practical grounds, but the latter disputed by a few
people. 

2'. slipping a date into the identifier - this is W3C's approach (e.g.
http://www.w3.org/2001/XMLSchema) though not clear that this is a fully
thoughtful position in relation to *XML Namespaces*, or is just a
consequence of W3C's URL design pattern which partly follows TimBL's
Cool URI's principles where he presented a weak argument for dating
everything. However, it does provide a potential snug home for
relatively coarse-grained versioning if required. 

Maybe a horses-for-courses case - different approaches apply to
different use-cases? 
Can we enumerate what these are?
Probably related to language volatility, and consequent maintenance
burden and capacity, 
which in turn is probably related to organisational capacity. 

Simon Cox

  

-----Original Message-----
From: xmlschema-dev-request@xxxxxx 
[mailto:xmlschema-dev-request@xxxxxx] On Behalf Of Eliot Kimber
Sent: Thursday, 12 May 2005 10:37 PM
To: xmlschema-dev@xxxxxx
Cc: Michael Kay; 'Dan Vint'; 'Fraser Crichton'; 
John.Hockaday@xxxxxxxxx
Subject: Re: Versioning of XML Schema and namespaces


Michael Kay wrote:
    

That's my reason for using the namespace with a version.

I understand all the stated reasons for not doing this, but 
        

out of the 
    

box there is nothing else that will consistently and automatically 
trip up validation if I don't have the "right" file being used to 
validate my documents.
        

You might make it easier for the recipient to do validation by 
including a version in the namespace, but you are making it 
      

hideously 
    

difficult for the recipient to process the incoming documents using 
namespace-aware tools such as XSLT and XQuery - as anyone who has 
tried to write code that handles the different flavours of 
      

RSS can tell you.

Yow! I completely forgot about this very practical reason for 
not versioning namespaces! This is really much more 
compelling than any philosophical argument I could make.

Mike is 100% correct--any namespace-aware processor, the most 
obvious example being XSLTs, may have to be significantly 
rewritten at the detail level in order to handle each new 
variant of the namespace for the same (abstract) application.

For example, consider this XSLT life cycle:

Time T[0]:

  - Application namespace is: xmlns:myns0="http://example.com/myns/v0"

  - Write template to match on element "foo" within "bar" in 
this namespace:

    <xsl:template match="myns0:bar/myns0:foo">

    (multiply by the number of element types in the application)

Time T[1]:

   - New version of the myns schema is released and the 
namespace is updated to: xmlns:myns0="http://example.com/myns/v1"

   - Rewrite *each* template to reflect the new namespace and the old
namespace:

    <xsl:template match="myns0:bar/myns0:foo | myns1:bar/myns1:foo">

    (multiply by the number of element types in the application)

  - Add any new templates for element types that are new (or in new
contexts) for this new release of the application.


Clearly this represents a huge maintenance cost for any non-trivial 
application and processor that needs to support multiple 
versions of an 
application. And multiple by the number of namespaces used in a given 
application--if all of them version their namespaces it's 
going to be a 
real mess within a short period of time.

By contrast, if the namespace doesn't change, new versions of 
the schema 
require only adding the specific code needed to react to 
those changes, 
not a change to, potentially, every match= and select= 
statement in the 
transform.

And note that using matches of the form "*[name() = 'foo']" are not 
generally safe when processing documents that contain elements from 
different namespaces because there could easily be conflicts of local 
names (that being the whole motivation for namespaces in the 
first place).

Cheers,

Eliot
-- 
W. Eliot Kimber
Professional Services
Innodata Isogen
9390 Research Blvd, #410
Austin, TX 78759
(512) 372-8155

ekimber@xxxxxxxxxxxxxxxxxxx
www.innodata-isogen.com


    

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