New SIA v2 proposal

[Markus Demleitner]

Hi Walter,

On Mon, Sep 07, 2015 at 12:51:25AM -0700, Walter Landry wrote:
> 1) The syntax for ranges uses NaN to indicate infinity.  I do not
> understand this at all.  NaN is not infinity.  Also, it provides no
> way to distinguish between positive and negative infinity.  We should
> use Inf, inf, Infinity, or infinity.

The NaN here is not infinity, it's NULL ("missing value").
Semantically, this is not "limit is infinity" but "there's no limit".
For floats, there's little difference, but I'd claim it's easier to
deal with a missing limit than to have to figure out all the
intricacies of IEEE floats[1].

The reason NaN is used here as a NULL literal is that we have a close
coupling of the SIAv2 HTTP parameter syntax to VOTables (e.g., you
can give defaults or limits for these in PARAMs in the service
metadata), and hence the agreement was to use VOTable tabledata array
syntax.  In VOTable, during the discussions leading up to 1.3, nobody
wanted to champion striking down the NULL=NaN convention we had there
since 1.0, and so I doubt anyone is too eager to open that can of
worms again.


> 2) RANGE: As I understand it, there have been 4 groups that
> implemented SIA v2 prototypes.  2 of them found RANGE useful, 2 of
> them did not.  As I have said before, RANGE is not needed and not
> always trivial to implement.  I do not think it should be required by
> the standard.

+1 from me on that, in particular since I've not found an actual
rebuttal of Walter's comment during public RFC on the SIAv2 RFC page;
all I can see is what to me sounds like agreement.  I know it hurts
to have to touch this document again, but from the RFC discussion I
would have expected RANGE to disappear, too.

Cheers,

         Markus

[1] Of course, with atomic parameters, all this would be a non-issue,
as there, a missing value would simply be represented by a missing
parameter.  But yeah, I've waved that ship goodbye, so... excuse this
wisecracking jibe.