This note describes the syntax for the various expressions for selecting data from the Measurement Set, implemented in the MSSelection²  module of CASACore. All expressions consist of a comma or semi-colon separated list of specifications. Except channel selection, the final product of parsing the expressions is a Table Expression Node (TEN) which can be used to construct a table with only the selected rows. Higher level global methods to return a selected table, given the user supplied expressions, are also provided as part of this module.

Error handling is done via the C++ exception handling mechanism. The exceptions thrown by the MSSelection module are of type MSSelectionError³  which is derived from AipsError class. The exceptions generated from each individual expression parser are further specializations of the MSSeletionError class. Application layer code therefore can have a finer level control on error handling. The module also support externally plug-able error handlers of type MSSelectionErrorHandler⁴ . This allows application layer code to have control on the resolution mechanism of the exceptional states that may be reached during the parsing cycle.

The MSSelection module can also be used for other tables that follow the general data base design of the MeasurementSet. The CASA CalTables⁵  is an example which also uses the MSSelection module for data selection.