Compound Mappings

[David Berry]

More comments on the draft Mapping doc at

http://hea-www.harvard.edu/~jcm/vo/docs/map.pdf

- Expanding on the italicised comment "My colleagues prefer the terms
SeriesMap and ParallelMap to CompositeMap and AggregateMap" in section
2.1 - my reasons for preferring "series" and "parallel" is that they give
more graphical descriptions of how the Mappings are combined, and
are possible more familar and clear to software engineers than the more
mathematical "Compose" and "Aggregate".

- Also on the subject of compound Mappings, I think that the
Series/ComposeMap and Parallel/AggregateMap classes should be derived
formally as sub-classes of a single parent "CompoundMap" class. This would
be another abstract class which inherits from Mapping. I hold this view
because the structure and methods of the two types of compound Mappings
can (and should?) be almost identical. That is, both types of compound
Mapping are basically structures which combine two or more Mappings into
another single Mapping, the only difference being how the Transform
methods are implemented in the two classes. They both have methods to
add Mappings and to return the member Mappings, and they can both be
simplified in the same way. They are virtually identical, and so it
would make sense to put all the common behaviour in a single parent
CompoundMap class.

More on the rest of the document to follow...

David

----------------------------------------------------------------------
Dr David S. Berry    (dsb at ast.man.ac.uk)

STARLINK project		 |	Centre for Astrophysics
(http://www.starlink.ac.uk/)	 |	University of Central Lancashire
Rutherford Appleton Laboratory	 |	PRESTON
DIDCOT				 |	United Kingdom
United Kingdom			 |	PR1 2HE
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