More separation - mirrors, copies, tight vs slack queries...

[Martin Hill]

There's a few things getting mixed here I think...

We can supply multiple interfaces to the same *instance* of a dataset, 
which is where Guy's proposed service-neutral description of the dataset 
is useful.  For example, the PAL library comes with amongst others, Cone 
Search, SkyNode (sort of :-), 'Full-Featured' SOAP, CEA, SIAP and soon 
SSAP interfaces.  Each of these requires a different entry in the 
Registry, but they are all just different interfaces to the same data.

There are also 'true' mirrors, where the data on a different bit of 
hardware is kept synchronised with the original one, and so we *could* 
have another deployed datacenter that might share the same table 
description. For example, at the ROE we have two different installations 
of SSA/USNO-B/2MASS.

'Copies' - where someone has taken a copy of the data and published it 
elsewhere - will need separate metadata documents because as additions 
or adjustments are made, the datasets will diverge slightly.  For 
example, the 2MASS at Edinburgh is not a mirror of that on the 
OpenSkyNode portal.

The issue of whether a cone search (or any other search!) runs on one 
specified table or 'any available table' merely describes how tight the 
search constraints are. And just to be argumentative (heh heh) I 
certainly don't see that as an astronomer vs developer difference - 
anyway from a developers point of view it's much easier when astronomers 
are explicit about what they want :-)

Cheers

Martin
(no, no storm please, not now)

Roy Williams wrote:

> From: "Tony Linde"
> 
>>  The same applies to data services: one service
>> might provide access to multiple data collections and one collection 
>> might
>> be served up by more than one service.
> 
> 
> As soon as the first cone-searches were built in 2002, we had URLs that 
> look like:
> http://blahblah.org/cgi-bin/cone?Catalog=Messier&RA=200&Dec=20&SR=10
> 
> Dissecting this URL, we can see two different semantically-distinct 
> entities:
> 
> (1) http://blahblah.org/cgi-bin/cone?Catalog=Messier
> This is an instance of a conesearch which queries a specific data 
> resource (the Messier catalog). It represents the point of view of an 
> astronomer-client.
> 
> (2) http://blahblah.org/cgi-bin/cone?
> This is a sort of "meta-conesearch", that can act as a consearch for a 
> number of data resources. It represents the point of view of a software 
> developer.
> 
> 


-- 
Martin Hill
www.mchill.net
07901 55 24 66
0131 668 8100 (ROE)