content, format, ctype, or xtype ?

[Doug Tody]

On Wed, 13 May 2009, Patrick Dowler wrote:

> So.... UCD?
>
> It looks like I object to everything but ucd: it allows one to say "this is a
> time". Maybe restriction is enough:
>
> MJD: DOUBLE <->  datatype="double" ucd="time"
> ISO8601: TIMESTAMP  <-> datatype="char" ucd="time"
> STC-S: REGION or POINT <-> datatype="char" ucd="pos" ?

While I agree with Alberto that in "strong" interfaces with formal
parameters and data models we often want to constrain the units and
representation, I question whether this is a good idea when we merely
want to expose arbitrary external data (such as tables).  In this case
it is probably best, as well as simplest, to make as few changes to the
external data as possible.  Hence unless we are populating the fields
of a well defined VO data model we should pass through whatever is
in the external data table, and merely aim to describe it accurately.

I wouldn't oppose using a UCD to identify something such as time in MJD
or ISO8601, but I don't think we should invent subtle linkages and
assumptions between UCD and datatype, meanwhile requiring data providers
to convert values in a data table.

So, another solution might be to merely use UCD, e.g., "time.iso8601"
or some such as Francois suggested (working up from #5 to #4!).

 	- Doug