VOUnits RFC

[Norman Gray]

Hello all: an addendum...

On 2013 Aug 1, at 14:59, Norman Gray <norman at astro.gla.ac.uk> wrote:

> This is looking dangerously like consensus!
> 
> It might be that the remaining points of discussion are to do with the language in the spec.  I'll make some revisions and make another version available.

To be clear, I think the consensus appears to be:

  1. The VOUnits syntax needs to be extended to add a numerical factor at the front.

  2. 'Unknown units' needs to be permitted in the syntax.

  3. Units may, but need not, be quoted with '...'; units thus quoted are immediately 'unknown' (even if they would otherwise indicate a 'known unit') and are not otherwise examined to detect prefixes.

  4. All unknown units can have all SI prefixes.

Re 1: there's still a bit of discussion necessary about the exact syntax of the float -- permissive or restrictive

Re 1: this means that there are now two exceptions to the aspiration that a VOUnits string will be parseable in all the other syntaxes, namely (i) the choice of '.' as the multiplication symbol is incompatible with OGIP, which uses '*', and (ii) the FITS and OGIP syntaxes only permit powers of 10, and the CDS syntax permits floats with a different syntax.  That's probably OK.

Re 1 and 2: the spec should include some text describing the disadvantages of both of these options; we may call this 'deprecation' or we may just call it 'usage advice'.

Re 2: The spec should say something about the QUDT units, and indicating that the VOUnits-specific 'known-units' are at different locations.  This is ripe for future standardisation.

Re 4:  This means that [k'martianDay'] and [kmartianDay] would both be acceptable and would be equivalent to each other.

Generally: The document should probably be clearer about goals and non-goals, using the discussion here as an indication of where clarifications should appear.  Rick's list of questions, earlier today, should all or mostly be answered in the spec.

How does that sound?  Have I missed anything (I'm pretty sure I have, but can't now recall what)?  Does anyone have particular suggestions for where clarifications should happen?

All the best,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
SUPA School of Physics and Astronomy, University of Glasgow, UK