  The table access protocol (TAP) defines a service protocol for accessing
general table data, including astronomical catalogs as well as general database
tables. Access is provided for both database and table metadata as well as for
actual table data. This version of the protocol includes support for multiple
query languages, including queries specified using the Astronomical Data Query
Language (ADQL [1]) and the Parameterised Query Language (PQL, under
development) within an integrated interface. It also includes support for both
synchronous and asynchronous queries. Special support is provided for spatially
indexed queries using the spatial extensions in ADQL. A multi-position query
capability permits queries against an arbitrarily large list of astronomical
targets, providing a simple spatial cross-matching capability. More
sophisticated distributed cross-matching capabilities are possible by
orchestrating a distributed query across multiple TAP services.
