content, format, ctype, or xtype ?

[Paul Harrison]

On 2009-05 -12, at 13:14, Mark Taylor wrote:

>
> I don't, any more than I think the fact that we require units as well
> as utypes should be regarded as a defect.  What I'm talking about is
> orthogonal to what utypes are for, which I take to be some kind of
> semantic characterisation.  In fact, it's more like what you've
> characterised as "lexical types" in your utype discussion
> (http://nxg.me.uk/note/2009/utype-questions/):
>
>   ... lexical types which indicate how a sequence of bytes is to
>   be parsed (is 123 intended to be the string ‘123’ or the
>   number 123 or possibly even a julian day number?)
>
> Two columns could have the same utype (indicating an observation time)
> but different [content/format/xtype/ctype/whatever-it's-called];
> one could be supplied as an ISO-8601 string, and another as an MJD.
> If I attempt your dereferencing trick and find out that the field
> I'm looking at is "like a date", it doesn't get me very far with that
> (even apart from the fact that I now need a network connection to
> make sense of an otherwise self-contained data file).
> Yes I can look at the datatype and have a guess, but this is messy,
> and it still doesn't help me distinguish between JD and MJD.



Can this concept not be satisfied by the units metadata for a column?  
There is a "units" effort going on within IVOA at the moment - if this  
prescribed the format for certain specialized units like MJD,  
sexagesimal etc. then there would be no need to add a piece of  
"format" metadata

Paul.