Table Access Protocol Window
The Table Access Protocol (TAP) load window can be opened using the TAP Query button () from the Load Window's toolbar or the Control Window's VO menu. It allows you to use the TAP protocol to make freeform queries of remote database services using an SQL-like language. This is a powerful capability, giving you full access to remote data holdings; it's similar to systems like SDSS's CasJobs, but using the IVOA-endorsed TAP standard means that you can use the same interface for many different remote datasets.
TAP is more involved than the other VO protocols implemented by TOPCAT, and this window is correspondingly more complicated than the Cone, SIA and SSA dialogues, though it does share some features with them.
In order to interrogate the remote database you will have to write queries in Astronomical Data Query Language (ADQL). This is a powerful tool, but to do complicated things in it is not trivial. ADQL is essentially a particular dialect of SQL, so if you know SQL already, you should be able to write ADQL queries. If you have used systems like SDSS's CasJobs, the concept should be quite familiar. A tutorial on writing ADQL/SQL is beyond the scope of this manual, but the Enter Query tab provides an Examples menu which will give you a good start in using it. You can find a nice introduction written by Markus Demleitner of GAVO at http://docs.g-vo.org/adql.
Once your query is written, you can submit it in either synchronous or asynchronous mode. Synchronous queries begin to execute right away and must be relatively short; asynchronous queries are submitted to a server, run for a potentially long time, and retrieve the result later.
The window is composed of four tabs, of which you can see one at a time. You will use two or three of them when submitting a TAP query. Each tab is described in more detail in the following subsections, but an overview of their operation is like this:
When you first visit this window, the Select Service tab will be visible, and when an asynchronous query has been submitted the Running Jobs tab will be visible. If you want to submit another query to the same service, or use a different service, just select Enter Query or Select Service respectively, by clicking on the appropriate tab at the top.
This window offers one menu additional to the standard VO windows menus:
The additional menu items are:
Note: The TAP dialogue has been introduced at version 3.8 of TOPCAT, at a time when most available TAP services are quite new and may not fully conform to the standard, and usage patterns are still settling down. For this reason you may find that some TAP services visible do not behave quite as expected; it is also possible that in future versions the user interface will change in line with changing service profiles or in the light of user experience.