On the "when" and "where"

[Paul Price]

> 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.

I agree that VOEvent needs to support a variety of coordinate/time
representations in order to cover all foreseeable events.  However, at
the same time, if the standard is too complex, you increase the
probability that implementations will be incorrect (e.g., a user
specifying UTC when he really meant UT1 or TAI; or J2000 instead of ICRS
--- the list of such subtle differences is near endless, and not every
astronomer knows what they all are).  Furthermore, the greater the
complexity, the greater will be the unwillingness of event providers to
invest in VOEvent when they can quite easily make up their own standard
that suits their own needs.

Might I suggest that the balance between these two philosophies
(maximalist/minimalist) could be reached by clearly specifying a set of
general default values.  For example, if a provider has RA, DEC and
DATE-OBS and wants to construct a VOEvent without mucking around, he
could stick them in, and everyone would understand that he's talking,
say, an ICRS position and a UTC time.  Then, if another provider wants
to refer to an event occurring at some latitude and longitude on Io at
some particular Solar System barycentric time, he still has the
capability with which to do so.

Forgive me if I'm naively wading in where you've been before.

Cheers,

Paul.
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