Using @version to indicate the schema version

[Markus Demleitner]

Hi Paul,

On Wed, Sep 05, 2018 at 12:55:06PM +0000, Paul Harrison wrote:
> There is something that I think needs to be borne in mind when
> considering this whole matter - the standard/schema can only have a
> minor change for this mechanism to be relevant - In reality I think
> that this will only extend to a x.2 version at most - it will be
> too difficult to find non-breaking additions to a protocol, so it

No, I don't think we should expect that.  The rules in schema
versioning are written such that we should be able to do quite a bit
of evolution, and that's a good thing because propagating changes in
namespace URIs is hard in the VO.

Take VOTable: Had we had the schema versioning policy from the start,
I'm pretty sure we'd still have the original VOTable namespace URI
from 2003 or so now, in version 1.3, and we'd try hard to keep it for
1.4.

> It is however possible that the actual schema document does have to
> have more updates (e.g. to fix technical errata) which was why I
> always had in mind that the xs:schema/@version had different actual
> content (see the uws schema as an example), though the original

Hm -- but then @version would again refer to the schema version
rather than the document/standard version.  And while for the latter
we have seen use cases (UWS), I'm still unsure there is a case for
annotating the precise schema version in document.

[I'm a big fan of using explicit redirects from the namespace URI to
URIs containing a full version, though.  That could be mighty useful
for debugging]

         -- Markus