The NExScI TAP Service¶
The primary expected audience for this document are services providers, usually those with existing relational DBMSs containing tables of astronomical data. A secondary audience would be end users of the service as we explain the details of connecting to the service and submitting queries. For example, the URL
is a complete synchronous TAP query that returns a list of all known exoplanets and their coordinates.
What is NExScI TAP?¶
Tabular data in astronomy (and other sciences) is commonly housed in relational databases. This may be final reduced data like astronomical catalogs or searchable metadata for image or spectra or anything else. Research projects very often start with database searches of these tables, often followed by the download of associated data files.
The International Virtual Astronomy Alliance (IVOA) Table Access Protocol (TAP) provides a standard interface specification for such queries. TAP defines how to compose the request using ADQL (a dialect of the standard Structured Query Language SQL), how to submit the request to a remote server (either in foreground or, for slow queries, in background), and how to retrieve results when they are ready.
The NExScI TAP service is a Python implementation of the protocol using open-source and extensible code. It is easy to install and configure and easy to extend to other DBMSs. NExScI TAP uses Python DB-API 2.0 to connect to DBMS servers. Currently connections to Oracle and SQLite3 have been tested with PostgresSQL and MySQL planned in the near future. If you have a particular DBMS you are interested in, please contact us.
Because queries against spatial regions on the sky are so common in astronomy, ADQL extends SQL with standard spatial constraint functions. In order to support these extensions, NExScI TAP includes a formalism for fast spatially-indexed searches which doesn’t require modification of the underlying DBMS.
Structure of this Documentation¶
NExScI TAP is aimed at operations of all scales, from a single table that a researcher wishes to share to the largest mission archives.
This documentation focuses initially on installation and configuration, then overviews TAP operations. There are several appendices covering the structure of the service, and delving into the details of the spatial indexing and the translation of ADQL into the local DBMS SQL.
For those who prefer to understand how things work before they start running them, most of the appendices have been written to make sense as stand-alone documents.
The NASA Exoplanet Science Institute is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.