VTP schema versioning updates

[John Swinbank]

Hi Markus,

Thanks for your comments — I am purely a dilettante at understanding the
details of XML, so I was hoping somebody like you would weigh in.

Markus Demleitner wrote on 2019-04-15:

> 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.

I don't _think_ I proposed doing this. My suggestion was that the schema
should live at the http://ivoa.net/xml/VTP-v2.0.xsd URL, but that it
contain the text:

  <xs:schema xmlns="http://www.ivoa.net/xml/VTP/v2"
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
	targetNamespace="http://www.ivoa.net/xml/VTP/v2"
	version="2.0">

My understanding was that this is consistent wth the XMLVers note,
but... per my earlier comments about dilettantism, I may be getting the
wrong end of the stick.

> 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.

So to back up a bit further, my understanding is that the current VTP
schema doesn't define a VTP-specific namespace at all: it simply starts
with a:

  <xs:schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns:xs="http://www.w3.org/2001/XMLSchema">

(and then never uses the “xsi” namespace).

By convention? historical accident? something like that, documents
claiming to comply with this schema (including the examples in the IVOA
rec) have contained the line:

  xmlns:trn="http://telescope-networks.org/schema/Transport/v1.1"

However, I'm not aware of the provenance of that line: there's no schema
I'm aware of that declares that as a target namespace, and the
telescope-networks.org domain is no longer hosting anything even
remotely relevant.

I therefore *am* suggesting that we change the namespace URI to refer to
an ivoa.net domain.

Is this a sane position, or should I move on with my life and do
something more productive instead?

Thanks again for your comments,

John
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