Spectral DM document update

[Doug Tody]

On Mon, 9 Oct 2006, Paul Harrison wrote:
> On 09.10.2006, at 15:51, Doug Tody wrote:
>> This approach would make sense, as not only is it more efficient
>> for large spectral arrays of several thousand points, it is more
>> consistent with the other serializations, which are also array-based.
>> Data handling and transformations between formats would thus be
>> more straightforward.
>> 
> I would argue that the whole point of the "pure XML" serialization is that it 
> is verbose - XML is intended to be self-describing and naturally 
> hierarchical, so expressing this serialization in a form that is as close to 
> the DM as possible would seem sensible - i.e. <Points> with all their 
> associated children rather than <Flux> with an array of points <Error> with 
> an array etc. If you want to be storage efficient then just use the FITS 
> serialization....

This is the usual approach with XML, and in general I agree, but in
this case we are talking about bulk data arrays which can be thousands
of points in length.  Ignoring for the moment efficiency concerns, it
is just a whole lot easier to deal with them as a single vector-valued
data element.  Plus as I say, this is more consistent with the other
serializations, facilitiating conversions, and with the likely use
of this data in applications code - which will probably also be
array based (all current spectral applications I am familiar with
are array based).

 	- Doug