Standardising units and formats (and ref frames?) in transmission

[Alberto Micol]

On 18 May 2009, at 11:19, Mark Taylor wrote:
> I agree that it would be very nice for data consumers if only a very few,
> very well-defined units and formats ever appeared in data coming over
> the wire.  But in some cases it will put a considerable burden on
> data providers.
In which cases?
Not just every possible field, just the most common ones,
like angles, times, wavelength, frequencies, magnitudes, and maybe few 
others...

It is not hard, just common sense in order to:
- slim down the number of otherwise necessary pieces of metadata
- boost Interoperability (more performant and less subject to 
interpretations/errors).
>   Since we do not have the power of obligation over data providers, 
But we do, when we come up with a standard;
I'm just asking the standard to be more interoperable.
> simply decreeing "time in VOTables will always be
> represented as ISO-8601 TT" (or whatever we come up with) will most
> likely have the effect that many data providers simply fail to comply,
> either providing VOTables for which this is not the case, or just
> giving up on VOTables/VO-blessed data formats altogether.
"Data passed through untouched" is easier for a data provider, obviously.
A web/html solution is good enough for that; why then do data providers 
need the VO?

But that means postponing the problem. Instead of being tackled by the 
knowledgeable provider,
the problem is left to the the end user, who very likely has less 
insight onto that piece of data.

I'm used to store RA and DEC in milli arcsec, FK5, J2000 (an old ESO 
practice);
a pass-through will present RA and DEC in milli arcsec to the users, and 
this is not what I want (nor ESO).
Hence, the input/output of any query is always translated back and forth.
This is very common practice across data providers, I do not see how 
that can be perceived as a show stopper.

At the contrary, I have already seen how data providers react to the 
IVOA standards:
there are so many options left for them to decide upon, that
(1) they get in despair,
(2) they call for a meeting to decide which way to go
(3) during the meeting they ask 5 colleagues and get 8 answers
(4) back to (1)
Postponing is not a good thing, even for data providers!
> I'm all in favour of encouraging data providers to provide position/
> time/whatever in certain standardised formats that we can decide on,
> I just don't think that uptake will be 100% (or even 90%), whether
> or not we call it a requirement. 
And Users will not be able to build their tools if they need an 
incredibly complex infrastructure
to make sense of any VOTable they receive.
(We are not the ones that will build the perfect tools for the astronomers:
for, as difficult as it is to admit it, they know better. ;-))

Alberto