VTP schema versioning updates

[Markus Demleitner]

Hi John,

On Sun, Apr 14, 2019 at 03:57:37PM -0700, John Swinbank wrote:
> - The schema is not available from the locations advertised in the VTP
>   standard (http://ivoa.net/xml/Transport/v1.1 and
>   http://ivoa.net/xml/Transport-v1.1.xsd).
> 
> To address this, I propose:
> 
> - To make a series of small updates to the VTP recommendation to resolve
>   the discrepancies.
> 
> - Following the above, to work with the IVOA to put the resultant schema
>   at http://ivoa.net/xml/VTP-v2.0.xsd (“VTP” being a less generic name
>   than “Transport”).

In namespace URIs, please don't include minor versions (any more).
Since you can't change a namespace URI without breaking clients,
doing that precludes having minor version updates.

All this is explained in more length in
http://ivoa.net/documents/Notes/XMLVers/.

So, assuming you actually want to change the namespace URI, what you
should do is: have a document VTP-v2.0.xsd defining the namespace
http://ivoa.net/xml/VTP2.

However...

> I'd be glad of any comments. In particular, note that this is purely a
> "book-keeping" change: it switches around namespaces and versions, but
> doesn't make any alteration to contents. As such, I'd like to solicit
> opinions as to whether it would be an appropriate erratum to VTP 2.0, or
> whether it requires a new version of the standard.

As claimed above, *if* your clients properly parse XML, they'll break
the second you change the namespace URI (see XMLVers if you don't
take my word for it), so technically you'd have to make it a major
version.  However, *if* all of your clients are written in a way
that they ignore the namespace declarations, I *may* be swayed to
look the other way during TCG review.

But still: Why risk breaking things?  We could easily arrange for
http://ivoa.net/xml/Transport/v1.1 (which is, I take it, the
namespace URI used throughout) and let it redirect to
http://ivoa.net/xml/Transport-v1.1.xsd (or, preferably, something
like http://ivoa.net/xml/VOEvent/Transport-v1.1.xsd, but that's not
important enough to warrant a change in documents containing the
other URL).  Yes, it's a bit unfortunate that this uses the fairly
generic "Transport" term, but if the TCG hasn't bothered to protest
back then, I'd say that's a fairly minor aesthetic defect.

         -- Markus