Version numbers on XMLschemata

[Ray Plante]

Hey Guy,

On Tue, 21 Nov 2006, Guy Rixon wrote:
> Can we _please_ not reuse XML namespaces with different content?

First of all, I *completely* agree with this request--well, mostly I 
guess.  Adding support for a new schema (i.e. with a new namespace) is not 
trivial for our applications; so care has to be taken.  Here are the 
conditions under which I've updated the schema files but not update the 
corresponding versions

   1.  changes only in documentation or formatting (e.g. spacing)
   2.  backward compatible changes that should not invalidate/break
          existing instances or applications
   3.  *minor* bug fixes that
         o  correct the schema to be consistant with what we been operating
            (because that's what we agreed to), and
         o  is not likely to invalidate the majority of existing instances
            or applications.

With the corrections I made after Moscow, all of the files except 
VOResource-v1.0.xsd fell into category 1.  The changes to 
VOResource-v1.0.xsd, I believe, fell into categories 2 and 3.  Now I may 
have gotten this wrong in this case.

I use the version attribute as a way to connect it with a version of the 
standards document that defines it.  I try to adhere to the practice of 
using the 3rd integer in the version to denote backward compatible changes 
that do not require a change in the namespace.

> Changing a schema and keeping the same namespace is way too disruptive.
> If many instance documents get out using different interpretations of the
> namespace it's downright tragic.

Changing the namespace in the context of registries--where we all have to 
use the same version for the critical schemas--is also extremely 
disruptive.  That's why I feel we need this middle ground.  Nevertheless, 
even if we don't think apps will break, we do need to announce even the 
minor changes.

If a change has a real effect on how our applications run, then--yes--we 
need to change the namespace.

> As Wil O'Mullane pointed out a while ago, vesion numbers are cheap and any
> time that we revise an exposed (= visible on web-site) artifact we ought to
> increment its version.

They are not cheap in the IVOA!  While the IVOA versioning rules are not 
suppose to apply to XML schemas, they will in practice if we define 
standard documents that define the schemas and their meaning.  The rules, 
then, impose a viscosity on the advancing of versions.

If you found that the changes did actually break things, I'd like to hear 
about it.

Sorry for the confusion,
Ray





>
> Cheers,
> Guy
>
> Guy Rixon 				        gtr at ast.cam.ac.uk
> Institute of Astronomy   	                Tel: +44-1223-337542
> Madingley Road, Cambridge, UK, CB3 0HA		Fax: +44-1223-337523
>