Timesys note review

[Mark Taylor]

On Wed, 28 Nov 2018, Markus Demleitner wrote:

> > Somewhat related: I think the discussion of the timeorigin attribute
> > in section 2 should be tightened up a little bit, so it's clear that
> > a value MUST be present for non-year-like time values as well as
> > saying that it MUST NOT be present for calendar-year-like values.
> 
> Hm, I see.  The trouble is that I don't think we can write
> 
> >    [...]
> >    which MUST be present when the time value being annotated represents
> >    an interval elapsed from an origin, such as MJD.
> 
> You see, any time specification represents an "interval elapsed from
> an origin", be it the Christian epoch, the mythical foundation of
> Rome, the Hijra, the launch of a space probe or (since I belong to
> the Church of Unix, my favourite) 1970-01-01T00.00:00Z.  So, I don't
> think this language works.  But I see the requirement level needs to
> be made clearer.
> 
> What about (svn rev. 5245):
>   
>   The timeorigin attribute MUST be given unless the time's representation
>   contains a year of a calendar era, in which case it MUST NOT be present.
> 
> (to see it in context: http://docs.g-vo.org/timesysnote.pdf, p. 4
> bottom; this doesn't have any language on the aliases yet)?

Yes, that's fine by me.  I wasn't that happy with the language
I suggested either.

--
Mark Taylor   Astronomical Programmer   Physics, Bristol University, UK
m.b.taylor at bris.ac.uk +44-117-9288776  http://www.star.bris.ac.uk/~mbt/