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Re: Versioning of XML Schema and namespaces

From: Fraser Crichton <fraser.crichton@solnetsolutions.co.nz>
Date: Mon, 23 May 2005 15:59:40 +1200
Message-ID: <4291552C.5050207@solnetsolutions.co.nz>
To: Simon.Cox@csiro.au
Cc: xmlschema-dev@w3.org
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>*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@csiro.au 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@w3.org 
>>[mailto:xmlschema-dev-request@w3.org] On Behalf Of Eliot Kimber
>>Sent: Thursday, 12 May 2005 10:37 PM
>>To: xmlschema-dev@w3.org
>>Cc: Michael Kay; 'Dan Vint'; 'Fraser Crichton'; 
>>John.Hockaday@ga.gov.au
>>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@innodata-isogen.com
>>www.innodata-isogen.com
>>
>>
>>    
>>
>
>  
>



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Received on Monday, 23 May 2005 03:50:58 GMT

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