3.4 Query VO using ObsCore TAP

Besides SSAP, SPLAT can also query VO services supporting ObsCore (Observation Data Model Core) components via TAP (Table Access Protocol). This services are known as ObsTAP services. There are two ways of doing that in SPLAT-VO by using a cone search interface, like the SSAP query, or by sending an ADQL query. ADQL stands for Astronomical Data Query Language, based on SQL. There are introductions and tutorials for ADQL for instance at http://docs.g-vo.org/adql (Markus Demleitner) or http://is.gd/ADQLTutorial (Simon Murphy).

Server Selection The server selection interface works in the same way as the server selection in the SSAP window. Just that the servers list contains ObsTap services instead of SSAP services, and there are no optional parameters, as all parameters can be queried using TAP.

Simple Search The simple search interface uses the same parameters as the SSAP cone search, with the same functionality.


ADQL Search The ADQL search is more flexible and more powerful than the simple cone search. The main part is a text area, which can be edited. The beginning of the query

SELECT TOP 10000 * from ivoa.Obscore WHERE dataproduct_type=’spectrum’

will get the first 10000 spectra from the selected servers. The TOP value may be changed to another value, if necessary. This query should be then refined or completed, either by choosing the parameters and expressions from the options provided (which will create a simple query) or by editing directly the the text area. Please refer to the ObsCore standard for the available parameters. (http://www.ivoa.net/documents/ObsCore/).

The example below shows a query for spectra including 6500 angstroms, spectral resolution better than 15 angstroms, spatial resolution better than 2 arcseconds FWHM, and exposure time longer that 3600 seconds:
SELECT * from ivoa.Obscore  
WHERE dataproduct_type=’spectrum’  
AND em_min < 650E-9  
AND em_max > 650E-9  
AND em_res_power > 6500/15.  
AND s_resolution < 2  
AND t_exptime > 3600

Implementation status

ObsCore and TAP are being developed by the IVOA (International Virtual Observatory Alliance2).