WD homework

[Patrick Dowler]

Just to bring everyone up to speed, the CSP "data cube access" solution 
being discussed is spread across several documents, with links to the 
latest drafts below:

1. WD-SIA-2.0 http://www.ivoa.net/documents/SIA/20131115/

This currently specifies the query capability with a minimal set of 
parameters. The use cases require that we add the ability to query by 
exposure time and spatial resolution as well as what is already 
supported (TBD).

2. WD-DataLink-1.0 http://www.ivoa.net/documents/DataLink/20140228/

This specifies two related things. The first is a service capability for 
returning multiple links froma single discovered identifier (usually 
expected to be the publisherDID from the ObsCore response). The second 
is a way to augment a votable with extra resources that describe service 
capabilities that can be invoked using the "things" in the table. 
Initial use is to augment the ObsCore output so clients can find and 
invoke the DataLink capability itself, other standard capabilities (eg 
the AccessData capablity below), and custom capabiliies/services.

3. WD-AccessData-1.0 http://wiki.ivoa.net/twiki/bin/view/IVOA/AccessData

This specifies a single capability that performs cutouts on data with 
input values in astronomical coordinates (RA and DEC, wavelength, time, 
polarization state). The whole idea is that the client makes one request 
to discover data and can make one or more requests to access individual 
data resources with the access(es) under client control. The access 
capability can be used after SIA2 query, after a TAP-ObsCore query, etc. 
This document is pretty minimal and re-uses the region-of-interest query 
params from SIA-2.0 query as that satisfies the minimal use cases. The 
plan is to add more functionality to this capability with future 
versions, so we don't need to do much here but we have to do it in a way 
that lets us add more later.

The DAL closing plenary from the Hawaii interop and the 2013B roadmap 
that may help explain where we are:

http://wiki.ivoa.net/internal/IVOA/PlenarySessionsSep2013/DAL-plenary2.pdf

http://wiki.ivoa.net/twiki/bin/view/IVOA/2013BRoadmap#Data_Access_Layer



The SIA query draft only species that the response conforms to the 
ObsCore  model/view. As it stands, ObsCore is undergoing some revision 
to reconcile with other DMs, specifically ImageDM. In order to keep DAL 
and DM specs from getting tangled up, we probably need a mechanism (like 
the one in TAPRegExt?) so SIA query can say which version of ObsCore it 
returns. Then when ImageDM comes along, implementions can start to use 
it. So that connection between data discovery and the model in the 
response needs to be thought about as well.



-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2E7

250-363-0044 (office) 250-363-0045 (fax)