The Napkin Representation (fwd)

[Silvia Dalla]

One more message in this thread.

---------- Forwarded message ----------
Date: Tue, 3 Jul 2007 16:06:30 +0100
From: Alasdair Allan <aa at astro.ex.ac.uk>
To: Roy Williams <roy at cacr.caltech.edu>
Cc: Silvia Dalla <s.dalla at manchester.ac.uk>, DM Mailing List <dm at ivoa.net>
Subject: Re: The Napkin Representation


Roy Williams wrote:
>Silvia Dalla wrote:
> >2. The simplest time series table consists of 2 columns only: one
> >giving the time and one giving the observable that is varying in time.
> >Is the new representation aimed only at this very simple time series?
>
>The motivation above would mean that the observable is a photon flux through a
>given transmission filter, expressed as magnitude or Jansky. So the current
>target is not about the general "time series", but rather about the much more
>specific "light curve".

Yes.

> >Or can the representation describe more complicated time series tables
> >that have a time column and several columns for different observables?
>
>As you know, the wider the scope of any standard, the more difficult it is to
>reach agreement. Thus, for the moment, the discussion has been about the simple
>case above.

I would say that the current napkin representation could easily have multiple
magnitude/flux values (and uncertainties) for each time stamp, e.g.

<Data>
   <Row number="1">
      <Time units="s" uncertainty="0.5">0/Time>
      <Flux type="mag" band="R" uncertainty="0.01">13.2</Flux>
      <Flux type="mag" band="B" uncertainty="0.02">17.4</Flux>
   </Row>
   <Row number="2">
      <Time units="s" uncertainty="0.5">35/Time>
      <Flux type="mag" band="R" uncertainty="0.01">13.3</Flux>
      <Flux type="mag" band="B" uncertainty="0.02">17.5</Flux>
   </Row>
     .
     .
     .
</Data>

in one of out suggested representations.

>In addition to flux, I have seen light-curves that include an attribute called
>"seeing", but that is still only two independent variables.

Hadn't realised that people wanted that, when was this mentioned?

Is a seeing measurement for every time step really necessary (i.e. for each
row)? or only per time-series, in which case it would easily be fitted into a
<Param /> inside the <Meta /> block. Of course you could generalise the params
and allow them to get inserted inside a <Row /> but at that point we've just
reinvented <VOTable> and we should probably forget about it. This is, at least
for me, about getting properly marked up light curves into my event data.

>Many people prefer a more rigid schema than VOTable provides, a more pure XML
>model.

Yup!

Cheers,
Al.