[Passband] diverting into SEDs

[Doug Tody]

> > BTW, I remember a Jonathan's document describing a bandpass datamodel.
> > What is the status of that document? Is this exercise a way to continue 
> > Jonathan's work?
> > I should read it again now, after few years ...
> 
> It's very readable, but covers a lot more than bandpass, and I feel (Jonathon 
> may disagree!) that it tends to mix up all the issues of modelling SEDs.  For 
> now, I just want to have a look at a part of it, then work up.  Also other 
> people have also done work, and I want to try and gather it all together from 
> the different areas.

A small component-style bandpass data model was defined about 2 years ago.
This was the basis for the bandpass model seen in SIA 1.0 query response.
Doug