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Requirements for the MS access classes

MeasurementSets are AIPS++ Tables and their existing access classes are built closely on the Table infrastructure. This assumption is implicit in the requirements listed in this section. The C++ classes used for MS access need to meet the following requirements, or provide the following services:

1.

Basic whole MS operations: MS creation, deletion and related MS-level operations.

2.

Column and row access: Access to MS MAIN and sub-table rows and columns.

3.

Sorting and selection: The ability to support bulk sorting and selection operations. MS selections are expected to be expressed in a close variant of the Table Query Language (TaQL), defined elsewhere.

4.

MAIN MS iteration: Sequential iteration through the MAIN MS table on arbitrary iteration indices, with optional retrieval of associated MS sub-table data matching the current MAIN table iteration interval. Indexed access to the MAIN table, on limited key indices, is a secondary requirement. MAIN table iteration includes simultaneous or sequential iteration through multiple MS considered as a set. Iteration is also required within MS MAIN rows, in frequency, velocity or polarization.

5.

MS sub-table iteration: Independent sequential iteration through individual MS sub-tables, on arbitrary iteration indices. Keyed access to MS sub-tables in read-write mode, on arbitrary key indices. Iteration is also required within rows, in frequency, velocity or polarization, as appropriate for individual sub-tables.

6.

MS derived quantities: Computation or retrieval of derived MS quantities, which require data access across the MS as a whole. Examples include elevation computation, assembling higher-level coordinate information or retrieval of Doppler shift parameters.

7.

MS data ranges: Determination of the data ranges in a given MS, for any MAIN or sub-table columns or derived quantities.

8.

MS data objects: Provision of C++ classes to model a data cube containing part or all of the current iteration or selection, which can be operated upon by other agent classes (e.g. calibration), and passed between AIPS++ classes and between C++ and Glish.

9.

Connection to Glish: Versatile access to the C++ MS access classes from Glish.

10.

Scratch column management: Creation and deletion of scratch columns which may be added to, or removed from the MS during reduction.

11.

Parallel I/O support: Full integration of parallel I/O capabilities within the standard serial MS access classes, and the ability to optionally enable the parallel I/O capabilities.

12.

Table infrastructure use: Full re-use of all Table system infrastructure and design philosophy wherever possible in the MS access classes.

13.

Efficiency: I/O is a critical part of astronomical data reduction performance, and efficiency is a key requirement for MS access. This includes integrated I/O profiling, in both the serial and parallel case.