SIAv2 mode [was: WD-SIA-2.0, going forward]

[Douglas Tody]

On Wed, 15 Jan 2014, Markus Demleitner wrote:
> I, frankly, cannot see any difference in total capabilities between a
> a service with both "mode" and accessData and accessData exclusively.
> There is nothing a client can do with mode that it couldn't do with
> accessData alone, no?

This is simply incorrect, as detailed in my previous emails.  With
automated virtual data generation (already present in SIAV1 for the past
12 years or so), a client can get analysis-optimized images from a
sufficiently capable service, with just a standard SIA query specifying
the region of interest, followed by a HTTP GET.  Furthermore they can
get them from multiple services simultaneously with a uniform broadcast
query, without having to know the details of the data being accessed, or
the details of the service capabilities, e.g., whether or not it
implements accessData and what is actually implemented.

It is much easier to do this sort of thing server-side than client-side.
It is unrealistic to expect that client software could ever deal with
the range of variability in data and data services (with many services
functioning inconsistently or implementing only a unique mix of
capabilities) required to do anything comparable.  Just look at where we
are headed now with queryData, ObsTAP, dataLink, AccessData, UWS, etc.
and expecting all this to be provided at every site, assuming all the
interoperable specs are even completed 1-2 years from now.  With SIAV1,
the AVDG capability is provided with a mere POS,SIZE query against a
cutout service followed by an HTTP GET.  SIAV2 (as originally proposed)
is still equally simple, just more capable.  It is important to keep the
simple things simple - we can add advanced capabilities and still
achieve this.  (Well, frankly I am beginning to seriously doubt that the
IVOA can).

 	- Doug