VOResource 1.1: Mirrors?

[Mark Taylor]

Markus,

On Tue, 14 Jun 2016, Markus Demleitner wrote:

> I took away from our mirrors discussion that
> 
> (a) people want the concept of mirrors in the registry,
> 
> (b) modelling each mirror as a separate resource is not appropriate
> for all the cases (in particular not for VizieR)
> 
> (c) there is no obvious candidate for metadata beyond the plain URL
> of the mirror.

Sorry I haven't engaged with this so far, but briefly: addition
of mirrorURL sounds OK, it's probably an improvement on not
having them.  However, presented with a bag of apparently
undifferentiated mirrors, it's hard to imagine how a
non-non-sophisticated client is going to make an intelligent
choice between them, unless it already has out-of-registry
information about the service.

The obvious thing is to present the list to the user and get them
to decide.  Thinking about the UI for that, some terse human-readable
information would be useful, e.g.:

   <accessURL use="base">http://example.edu/svc/stars?</accessURL>
   <mirrorURL use="base" description="Primary backup" >http://example2.edu/svc/stars?</accessURL>
   <mirrorURL use="base" description="European mirror">http://example.de/svc/stars?</accessURL>
   <mirrorURL use="base" description="Italian mirror" >http://example.it/svc/stars?</accessURL>

I don't think we know enough about machine use of these things
yet to codify any machine readable vocabulary for mirror function.
I am tempted to suggest another attribute that could serve as a
placeholder for such machine readable information, without specifying
any content for it now, in case we think of a way to do that in the
future and don't want to update VOResource, e.g.

   <mirrorURL use="base"
              description="Primary backup"
              mirrortype="ivo://ivoa.net/std/VOMirror#backup1"
              >http://example2.edu/svc/stars?</accessURL>
   <mirrorURL use="base"
              description="European mirror"
              mirrortype="ivo://ivoa.net/std/VOMirror#geo-by-continent"
              >http://example.de/svc/stars?</accessURL>
   <mirrorURL use="base"
              description="Italian mirror"
              mirrortype="ivo://ivoa.net/std/VOMirror#geo-by-tld"
              >http://example.it/svc/stars?</accessURL>

but that may be getting a bit adventurous.

> I feel a bit bad for doing this, as I don't see that any software
> might use this by the time I'd like VOResource 1.1 go to REC, and
> nothing to go to REC that's not been tested in use.  So, if a client
> author volunteers, I'd be happy to work with you.

I'm not promising, but: before clients can use it, there would
need to be some of this content in the registry to test it on.
Is that likely on the time scale you've got in mind, and if so for
what types of service?

Mark

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/