IVOA Recommendation: IVOA Astronomical Data Query Language Version 2.00
  This document describes the Astronomical Data Query Language (ADQL). ADQL has been developed based on SQL92. This document describes the subset of the SQL grammar supported by ADQL. Special restrictions and extensions to SQL92 have been defined in order to support generic and astronomy specific operations. 
Inaki Ortiz, Jeff Lusted, Pat Dowler, Alexander Szalay, Yuji   Shirasaki, Maria A. Nieto-Santisteban, Masatoshi Ohishi, Will...
astro-ph.IM