3. A First Query

To follow the examples, start TOPCAT and select TAP in the VO menu. Click the pin icon in the upper right corner of the dialog to keep the query window open even while the query is executing..

At Keywords type gavo. Wait until the results are filtered and select the Gavo Datacenter. Then click “Use Service".

You already made use of the VOs

"google"like service: the registry. A rough introduction of the registry how you can use it for data discovery will be explained in chapter"Data Discovery".

At the bottom of the form, at Mode: check

"Synchronous"and enter
SELECT TOP 1 1+1 AS result FROM ivoa.obscore

in the text box, then click

"Ok". This should give you a table with a single 2 in it. If that hasn’t worked complain.

Copying and Pasting from http://docs.g-vo.org/adql is legal.

Note that in the top part of the dialog there’s metadata on the tables exposed by the service (in particular, the names of the tables and the descriptions, units, etc., of the columns). Use that when you construct queries later.

There are other TAP clients than TOPCAT – after all, we’re talking about a standard protocol. Another TAP client widely used is Aladin.

An emulated command-line database shell is tapsh; most of the queries here assume you’re querying against the server with the IVOA id

ivo://org.gavo.dc/__system__/tap/run.

To get that, typing server ivo://org.g and then completing with Tab should be sufficient.

You can also use TAPHandle, which runs entirely in your browser.

For running a TAP client in scripts there is STILTS or PyVO

More TAP clients can be found on the IVOA applications page.

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Markus Demleitner

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