An STC "when" and "where" example

[Arnold Rots]

Just to answer a few points:

Why is that document not valid?  It doesn't validate with the schema.
That, I believe, was the question and hence the simple answer.

Defaults have the nasty habit of making people forget they are there,
with disastrous consequences when they are used by mistake.
Also, defaults that are tailored for one part of the community (which
they inevitably are) tend to infuriate other parts since they feel
discriminated against - not unreasonably.

In a sense, we are offering a flexible default system by compiling a
library of XML documents suitable for XInclusion.  If your parser sees
the include of ICRS-TT-WAVELENGTH-TOPO.xml, or the use if an ID by
that name, for an AstroCoordSys, it can elect to skip reading that
element and insert a set of defaults that corresponds to that system.
If all you care about is the ICRS part, then ICRS-UTC-FREQ-GEO.xml
would provide you with the same information.
Since the use of such a standard library amounts to registering a
collection of standard IDs, you might write a parser that completely
ignores the includes and knows which IDs it can handle and which it
can't.  But formally the information is there for anyone who wants the
gory details - and no one can say: I didn't know what you meant.

I must say I take exception to an attitude that says: if you need more
details than I bother to provide, that's tough luck for you -
don't use my events.

  - Arnold


Alasdair Allan wrote:
> 
> Arnold Rots wrote:
> > What you have there is not a valid document.
> 
> Pity! Why not? Where does it fall over?
> 
> > I'm a bit puzzled, though, why someone would want to use VOEvent to
> > just transmit a position...
> 
> It's fairly fundamental. If I'm sending an alert that is going to
> >  might as well send e-mail saying:
> 
> Email? For most purposes a VOEvent object will be serialised into an 
> XML document and pushed over a SOAP connection
> 
> > "RA, Dec: 148.88821 69.06529"
> > I would have thought that providing a time,
> 
> Time isn't necessary under all circumstances.
> 
> > wavelength,
> 
> Wavelength isn't necessary under many circumstances.
> 
> > observer's location,
> 
> Not necessary in many circumstances.
> 
> > and errors would be essential.
> 
> Errors are always helpful, but not necessary in all cases.
> 
> > STC-X does not allow defaults, in general, the reason being
> > demonstrated by what you wrote: those defaults sounded very reasonable
> > to you, but I would have chosen rather different ones.  Since the VO
> > intends to tie together many subcommunities, the use of defaults is
> > dangerous.
> 
> Defaults are necessary, the defaults can be specified as part of the 
> standard and therefore everyone uses the same defaults and there is no 
> danger.
> 
> > Giving minimal, sketchy information may be fine for some of your
> > clients because they know exactly what you mean or they don't require
> > great accuracy, but there may be other potential clients who cannot do
> > anything with it because there isn't enough information; the planetary
> > community is an obvious example.
> 
> Then they should ignore the document as it doesn't have enough 
> meta-data for their purposes, those clients that can make use of the 
> document can do so...
> 
> > As to your stripped-down version, I can make a similar one that is
> > valid by using XIncludes and I have appended that one at the end of
> > this message.  Three more lines than yours, one of which I promise to
> > get rid of in the next version of the schema.
> 
> That looks a bit better, although I still don't understand your 
> instance on including bandpass information for a time and co-ordinate 
> representation.
> 
> > Any parser that feels like it (or knows what they say) can skip the 
> > included documents which are going to be part of a standard IVOA 
> > library.
> 
> Sorry, I have to take issue with this...
> 
> Are you going to sit down and write factory and parser toolkits in 
> Perl, Python, Ruby, C, C++, C#, Fortran, Java, PHP and the half dozen 
> other languages currently in use inside various projects that will be 
> involved in creating and parsing VOEvent messages?
> 
> Just because the majority of the VO was written in Java doesn't mean 
> the whole world uses Java. VOEvent is designed to go outside the 
> carefully crafted VO infrastructure. People who have never heard of the 
> VO might be interested, for the first time, in some of the stuff we're 
> doing here. The buy-in for VOEvent has to be small, minimal.
> 
> Al.
> 
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Arnold H. Rots                                Chandra X-ray Science Center
Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
60 Garden Street, MS 67                              fax:  +1 617 495 7356
Cambridge, MA 02138                             arots at head.cfa.harvard.edu
USA                                     http://hea-www.harvard.edu/~arots/
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