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## 6 Virtual Observatory Access

Several of the windows in TOPCAT allow you to interface with so-called Data Access Layer services provided within the Virtual Observatory (VO). The buzzwords are not important, but the basic idea is that this allows you to locate a service providing data which may be of interest to you, and then query that service to obtain the data. The VO is not a single monolithic entity, but a set of protocols which allow a general purpose tool such as TOPCAT to talk to services made available by many different participating data providers in a uniform way, without having to have prior knowledge of what services are out there or the details of how their data is arranged.

The basic operation is similar for all of TOPCAT's access to these services:

1. Select the registry to query for services (or use the default one)
2. Query that registry for services of interest
3. From the returned list of services, select one that you wish to query for data
4. Specify the query to send to the data service
5. Start the query and wait for the result

These ideas are explained in more detail in the following subsections. The windows from which this is done are documented in Appendix A.9.

Note: For information on SAMP, which is a protocol developed within the Virtual Observatory context, but are not necessarily concerned with remote data access, see Section 9.

- 6.1 The Registry
- 6.2 Data Access Services

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk