(Note that I have changed the subject line for this topic which had previously  piggybacked on the thread " Re: [DATETIME] Extended Date/Time Format DRAFT specification for review through December 6")

I would like to suggest an approach to address the "season" requirement, based on numerical values for seasons.  I suggest 21-24 (as suggested by John Hostage and as used in marc holdings).

Thus 21, 22, 23, 24 would mean spring, summer, autumn, winter, respectively.  This means the first season is always spring (unless qualified by a location, see below).

So where the string '2000-12'  means "december, 2000", the string '2000-21' could mean "spring, 2000" which would be unambiguous since 21 is not a valid month. Even so, I think we should add an explicit season indicator, thus:


Although whether to use parentheses or some other delimeter there, I haven't completely analyzed.  

Now if you want to represent "spring 2000 australia"


However, I don't know exactly what vocabulary we want for the geographic designator.  Country?

And if you want to represent  "spring/summer":


The main issue here is maintaining sortability, so we have to choose the delimiting characters carefully (which I haven't done yet).

Yet another issue is "quarter" vs. "season".  Other than saying: "21 means spring or first quarter; 22 means summer or second quarter, etc"  I'm not sure know how to address this.  We could assign a different set of numbers, but then you wouldn't be able to sort, if you have a mix of issues. But maybe that's not a requirement. 

Another point. In the case where  the first season is winter, and where (as I take it from this discussion) this is inferred from the geographic designator, sorting is obviously not going to work.

One more: in the very simplest case, just a year and season (no geographic designation, etc), would it be reasonable to allow both representations:
'2000-21'  and 'season(2000-21)'?

Other issues?

Please comment.