The Napkin Representation (fwd)

[Silvia Dalla]

cc-ing to the VOEvent list too.

---------- Forwarded message ----------
Date: Tue, 03 Jul 2007 07:53:41 -0700
From: Roy Williams <roy at cacr.caltech.edu>
To: Silvia Dalla <s.dalla at manchester.ac.uk>
Cc: DM Mailing List <dm at ivoa.net>
Subject: Re: The Napkin Representation

Silvia

Thank you for asking all these very relevant questions about the current
standards effort for time series that is taking place in the IVOA Data Modeling
working group.

> 1. Is this representation aimed at Time/Flux time series only,
> or should it be catering for time series of other quantities too?
> (orbits of objects have been mentioned by others earlier).

My understanding is that several sites are setting up archives of light curves
from astrophysical sources, so that they can be queried and mined as usual, but
also for comparison with observed data from transient sources for
identification. The real and proposed light-curve archives that I know of are:
ESA Madrid, CfA Boston, UC Berkeley, perhaps others can tell us of others.

> 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".

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

> > (of course, I still don't see why a VOTable wouldn't work, but that was my
> > chief objection at the HTN/VOEvent meeting where The Napkin was wrote upon,
> > blessing us all with The Napkin Representation, but hey... :-) )
>
> For those that were not at the HTN meeting it would be useful to know
> what are the objections against using a VOtable representation.
Many people prefer a more rigid schema than VOTable provides, a more pure XML
model. But I do not see VOTable as a necessary part of a standard, it is just a
representation. It is the names of quantities and what they mean, that is the
important part. Think of translating base 2 numbers to base 10, it is easy to
do, it is just representation.

Cheers
Roy