Spectral DM document update

[Paul Harrison]

On 09.10.2006, at 15:51, Doug Tody wrote:

> On Mon, 9 Oct 2006, Jonathan McDowell wrote:
>
>> I've incorporated the recommendations from Moscow
>> into the Spectrum document; it's at
>> http://hea-www.harvard.edu/~jcm/vo/docs/spec98/spec98d.pdf
>> There have been no changes to the list of UTYPEs but I have
>> added mandatory/recommended/optional markers, and altered the
>> FITS part following comments from STScI.
>
>> I have not yet addressed the issue of the XML schema serialization
>> of the data segment: the two alternate versions include a simple
>> XML <Point>.... </Point> which is very verbose, and a more compact
>> attribute-laden Point which was developed following Lazlo's example
>> in the JHU service. However Lazlo himself suggested that we replace
>> this with arrays like <Flux>1.2 1.3 1.4 ... </Flux> where all data
>> point attributes are in separate arrays, instead of having
>> Point No. 1 (flux, err, spco, ...) then Point No. 2 (flux, err,  
>> spco...)
>> etc. I didn't get much feedback in Moscow about whether this was
>> considered by others to be a good idea, since the email discussion
>> got sidetracked onto the format-specifying issue that Lazlo raised
>> in the same email.
>
> 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.
>
> 	- Doug

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....

Paul Harrison
ESO Garching
www.eso.org