On the "when" and "where"

[Rob Seaman]

Alasdair Allan wrote:

> Pardon? If you embed an STC structure inside an VOEvent document, a 
> parser developed to read and write VOEvent documents also has to 
> understand STC documents. If you want to handle a VOEvent document you 
> need a parser, I don't understand what your argument is here...?

Your argument isn't with me, it isn't with STC - your argument is with 
the notion of VO having any coordinate/time standard at all.  If VO has 
a standard way of representing coordinates, why wouldn't VOEvent make 
use of it?  If that standard is inappropriate for VOEvent, it likely is 
inappropriate for other purposes and should be improved.  Personally, 
STC seems to me to have performed a magic trick in avoiding the world 
coordinate pitfalls that have entertained us in FITS for years.

> if it makes too many demands on the developers it won't get used. 
> People won't implement it fully, you'll end up with conflicting 
> partial implementations  of VOEvent that dont't interoperate and it 
> won't get taken up. We need an absolute minimal buy in here...

I'd omit the word "absolute", but I agree.  VOEvent needs to support 
the simplest possible coordinate and time format.  I would argue that 
the way to do this is to make a VOEvent a vessel (to avoid the loaded 
word "container") for a separate coordinate/time data structure.  I 
would further argue that STC is that data structure, but perhaps the 
convened big domes will deem that VOEvent has to support something else 
simpler *in addition to* STC.

I think it does matter whether the coordinate/time data structures are 
highly integrated into each VOEvent.  I think it does matter whether 
the coordinate/time data structures are constructed by the VOEvent 
layer/component, or rather, by the calling entity.

Again, either VOEvent supports a rich enough set of coordinate/time 
representations to convey all possible astronomical events - or VOEvent 
should be explicitly limited to only a pre-specified list of event 
types.  We can't have it both ways.

Rob Seaman
NOAO