SIAV2 prototype / reference implementation

[Douglas Tody]

Hi DALers -

If you want to try out the developmental/reference implementation of our
SIAV2 prototype you can exercise the service yourself at the following
link:

     http://vaosa-vm1.aoc.nrao.edu/ivoa-dal/siav2query.html

This is just a crude Web interface used to test the prototype, but it
provides an easy way to see how it all comes together.  The query
response should render as a VOTable in your Web browser.

In the current version the MODE parameter, used to enable cutout mode
(and what I will be mostly focusing on in my talk in the DAL/DM session
later today), is disabled.  While most of the functionality for this is
implemented in the prototype service, it was not finished in time to be
deployed to the demo service in time for this meeting.

However the way it will work is simple enough: if for example one issues
a query with "MODE=archival,cutout", the query response will be what you
see now except that for each archival image for which a cutout is
possible, there will be an additional row in the query response
describing the cutout virtual image.  The metadata for the cutout image
will describe the image that will be created if retrieved via the access
reference.  No datalink is required in this case since the cutout image
is described directly in the query response, and already has an access
reference URL for retrieval.  All image retrieval, including retrieval
of archival images as well as virtual image generation, is performed by
the accessData request (the access reference URL returned in a query
response is actually a call to accessData).  AccessData can also be
called explicitly by a client to directly access a particular image
identified by its publisher dataset identifier.

 	- Doug