... specification¹

MSSelection module is currently used to only parse the channel selection expression to produce the START,STOP,STEP tuples. No channel based selection is actually applied to the data. The list of tuples per SPW is passed to the application program layer and the interpretation of the tuples for actual selection depends on the application programmer.

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... data²

The combined main-table descriptor for spectral windows and polarization is the Data Description ID (DDID). DDID represents a two-level indirection based on the the Spectral Window and Polarization sub-tables (which are the real astro-physically relevant parameters of the database).

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...[SPW:]POL³

A full specification of the type [[POLID:][SPWID:]POL or [DDID::]POL will be implemented in future.

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...=INT"⁴

Programmers note: The getScanList() (getSubArrayList() for sub-arrays) method will return the list generated from INT,INT,... or INT$\sim$ INT or "$<$ INT" specification. For "$>$ INT" specification, the returned list will be number from INT part of "$>$ INT" upto the maxScans (maxArrays for sub-arrays) set via MSSelection::setMaxScan() (MSSelection::setMaxArray() for sub-arrays). The default value of maxScans/maxArrays is std::standard_limits$<$ int$>$ ::max() (i.e. the maximum value an integer can take on a machine). It is done this way since there is no efficient way of generating a list of SCAN/ARRAY IDs present in the data and "$>$ INT" is an unbounded list of integers. The list of scans IDs in the data can be probably generated using the MSRange class - but I think it can be quite expensive. So if it is necessary to know the precise list of scans selected using the "$>$ INT" specification, the application programs will have to use MSRange class to get the range in the data. An intersection of the list from MSRange and the list from MSSelection.getScanList() will be the actual selected scans (intersection of two CASA vectors can be done using the set_intersection() global method in MSSelectionTools.h).

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