The Napkin Representation
roy at cacr.caltech.edu
Tue Jul 3 07:53:41 PDT 2007
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
>> 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.
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