TaQL.h

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// # TaQL.h: The TaQL module - Casacore data querying
// # Copyright (C) 1994-2010
// # Associated Universities, Inc. Washington DC, USA.
// #
// # This library is free software; you can redistribute it and/or modify it
// # under the terms of the GNU Library General Public License as published by
// # the Free Software Foundation; either version 2 of the License, or (at your
// # option) any later version.
// #
// # This library is distributed in the hope that it will be useful, but WITHOUT
// # ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
// # FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
// # License for more details.
// #
// # You should have received a copy of the GNU Library General Public License
// # along with this library; if not, write to the Free Software Foundation,
// # Inc., 675 Massachusetts Ave, Cambridge, MA 02139, USA.
// #
// # Correspondence concerning AIPS++ should be addressed as follows:
// #        Internet email: casa-feedback@nrao.edu.
// #        Postal address: AIPS++ Project Office
// #                        National Radio Astronomy Observatory
// #                        520 Edgemont Road
// #                        Charlottesville, VA 22903-2475 USA
 
#ifndef TABLES_TAQL_H
#define TABLES_TAQL_H
 
// # Includes
// #   table expressions (for selection of rows)
#include <casacore/casa/aips.h>
#include <casacore/tables/TaQL/ExprNode.h>
#include <casacore/tables/TaQL/ExprNodeSet.h>
#include <casacore/tables/TaQL/TableParse.h>
 
namespace casacore {  // # NAMESPACE CASACORE - BEGIN
 
// <module>
 
// <summary>
// TaQL is the query language for Casacore tables
// </summary>
 
// <use visibility=export>
 
// <reviewed reviewer="jhorstko" date="1994/08/30" tests="" demos="">
// </reviewed>
 
// <prerequisite>
//    <li> <linkto module="Tables:description">Tables</linkto> module
// </prerequisite>
 
// <etymology>
// "TaQL" is the Table Query Language. Its pronounciation rhymes with bagel.
// </etymology>
 
// <synopsis>
// TaQL is an SQL-like language to query a Casacore table.
// Amongst its options are row select, sort, update, and delete.
// <br>Some more information is given in the description of the
// <linkto module="Tables:select and sort">Tables module</linkto>.
// A detailed description is given in <A HREF="../notes/199.html">note 199</A>.
//
// The high-level interface is using a TaQL command as described in
// <A HREF="../notes/199.html">note 199</A>. Such a command can be given
// in C++ (using TableParse.h), Python or the shell program 'taql'.
// The code for parsing and executing TaQL commands is quite complex.
// Processing a command consists of two steps.
// <ol>
//  <li>
//  First a command is parsed using 'flex' and 'bison'. The file TableGram.ll
//  is used by 'flex' to recognize the tokens in the command. The file
//  TableGram.yy defines the grammar which is used by bison to invoke
//  actions on the recognized parts of the command. These actions
//  consist of building a parse tree by means of class TaQLNode and
//  associated classes. In this way the command is syntactically checked.
//  <li>
//  If the parsing is done successfully, the command is executed
//  by walking through the parse tree using class TaQLNodeHandler.
//  In its turn that class invokes functions in class TableParseQuery
//  to check (semantically) and execute commands such as SELECT, UPDATE, etc..
//  Note that subqueries are executed before the entire parse tree has
//  been walked through, thus before possible later semantic errors are
//  detected.
//  <br>Expressions in the parse tree are converted to expression trees
//  using the various TableExprNode classes. Expression trees are evaluated
//  for each row in a table. Note that expressions can be used in many
//  parts of a TaQL command.
//  Functions in a command are handled by TableParseFunc.
// </ol>
//
// Expression trees can also be generated directly in C++ using class
// TableExprNode which is overloaded for many operators and functions
// (such as sin, max, etc.). In fact, TaQLNodeHandler uses this code.
// For example:
// <example>
// <srcblock>
//    Table tab("my.ms");
//    Table selection (tab(tab.col("ANTENNA1") == tab.col("ANTENNA2")  &&
//                         tab.col("SPECTRAL_WINDOW_ID") == 0));
// </srcblock>
//  creates a (reference) table containing the autocorrelations of the
//  first spectral window in "my.ms".
// </example>
// </synopsis>
// </module>
 
}  // namespace casacore
 
#endif