[Fwd: VOTimeSeries]

[Rob Seaman]

Francois replies to Roy:

>> QUESTION: What semantic information is MISSING from this time series?
>> QUESTION: Is there TOO MUCH metadata here, is it too COMPLEX?
>> QUESTION: What other syntax could be used besides VOTable?
>
> Just take care of the comments -- TimeObs tells it's the "Modified  
> Heliocentric Julian date of mid-exposure" but the value indicates  
> 1305, corresponding to 14 June 1862, 145 years ago...

Is bounds checking to be part of the DM?  There is nothing  
intrinsically incorrect about conveying a nineteenth century  
dataset.  The magnitude scale (and hence the potentiality of a light  
curve) originated with Hipparchus.  De Stella Nova expressed in 1573  
that stars vary in brightness.  Anybody have a candidate for the  
earliest published light curve or time series?

> There seems also to be some contradictions in the time units --  
> TimeStart and TimeDate are indicated in 'd' (days),

The clock is a subdivision of the calendar, so time can be given in  
units of days.  (This is the crux of the ongoing UTC leap second  
debate.)  The bigger issue is that date and time must form an atomic  
whole.  Perhaps the best way to eliminate this issue is to avoid  
"time" fields entirely in favor of "date" analogs as with FITS DATE-OBS.

> TimeObs has no unit (but a wrong comment); the time series itself  
> indicates 's' as units for Time (top table), but the values given  
> for the time in the examples (middle table) seem to be days elapsed  
> since the TimeZero.

For some reason, perhaps because clocks and calendars seem "obvious"  
while telescope setting circles do not, self-consistent time usage  
continues to elude us even as esoteric WCS usage proves tractable.

My own two cents is to second Doug's comment:

>>> Since the data model is defined independently of the  
>>> serialization, there is no need to pick a single serialization.

Which I understand to imply that VOEvent - an XML publication  
standard - might settle on a distinct time series representation from  
other VO applications relying on CSV, FITS, native VOTables, or  
"graphical rendition" (e.g., IRAF GKI metacode, I suppose).

Rob
seaman at noao.edu

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