CADC TAP service released

[Patrick Dowler]

I would like to announce to everyone the release of the CADC TAP service for 
querying our observation database. The base URL for the service is:

http://www.cadc-ccda.hia-iha.nrc-cnrc.gc.ca/caom/

We have implemented all of the child resources:

/caom/async           -- async querying using UWS pattern
/caom/sync             -- sync querying using GET or POST
/caom/availability  -- VOSI availability
/caom/capabilities -- VOSI capabilities
/caom/tables          -- VOSI tables

Most of the software to implement our TAP service is open-source and 
available at http://opencadc.googlecode.com/ . We tried our best to make the 
code there extensible and customisable without modifying it directly, and we 
tried to leave people free to pick and use parts of the libraries without 
buying in to the whole thing.

* content *

The main content of the service is the Common Archive Observation Model 
(CAOM) in use throughout most of CADC. We have implemented this model in 
the following collections: BLAST, CFHT, HST, IRIS, JCMT, and MACHO (1.33 
million observations and ~4 million different products).

The service includes a prototype implementation of the ObsCore model being 
developed as part of the ObsTap project from the take-up committee. The 
prototype includes a table (well, view) called ivoa.ObsCore; it is not fully 
populated.

We have a view called caom.SIAv1 which provides access to just calibrated 
images; this view is used by our new SIA service(s); users that query this 
view will get output compatible with the SIA 1.0 specification (required fields, 
UCDs, etc) and this is exactly what our new SIA service does.

Note that caom.SIAv1 and ivoa.ObsCore are both views that include joins to 
the caom.Plane table so these provide three different ways to access the 
same content.

There is also a complete TAP_SCHEMA there to query and discover the CAOM 
model; this content is also available via /caom/tables.

* implementation details *

The back-end database is PostgreSQL with the pg_sphere extension.

We currently support LANG=ADQL only. The ADQL supports complete 
ADQL geometry support (although the BOX support is poor) including the 
REGION function and STC-S. Output also uses STC-S for the position_bounds 
column of our model.

We support output in VOTable, CSV, and TSV formats, although only VOTable 
has a mechanism to indicate that the result was truncated (by default or 
specified MAXREC).

We do not yet support UPLOAD; we started but it is quite hard to safely create 
tables, read content, and insert it into a database.

Since our database contains proprietary data and proprietary metadata, the 
query execution includes some fine-grained access control. This is not yet 
fully implemented, so some queries may fail because they run into the limits 
of our access-control implementation. We are working on this, but for now 
queries must include one of caom.Plane, caom.SIAv1, or ivoa.ObsCore tables 
in the from clause. 

PS-I am sure there are still bugs :-)

-- 

Patrick Dowler
Tel/Tél: (250) 363-0044
Canadian Astronomy Data Centre
National Research Council Canada
5071 West Saanich Road
Victoria, BC V9E 2M7

Centre canadien de donnees astronomiques
Conseil national de recherches Canada
5071, chemin West Saanich
Victoria (C.-B.) V9E 2M7