content, format, ctype, or xtype ?

[Norman Gray]

Greetings.

On 2009 May 11, at 13:48, Mark Taylor wrote:

> As far as TOPCAT can tell, the column contains a string, and so it is
> unable to make a plot with it, or otherwise do anything much apart
> from display the string contents.  If it understood that the column
> contained a string with the semantics of an iso-8601 date/time,
> it could make this plot.  Yes it may be possible to glean this
> information by inspecting the utype, but in order to do that it needs
> to have an understanding of the data model in question - a lot of work
> for the developer, and needs to be updated every time a new data model
> appears or is modified.  Moreover, the additional, probably rather
> detailed, information supplied by the utype is not relevant for this
> kind of processing.

Earlier, Rob pointed towards the utype suggestions I made a while ago <http://www.ivoa.net/Documents/latest/utype-uri.html 
 >.  These suggestions address this, in the sense that they describe  
how, if an application comes across an element annoted with a utype it  
does not recognise (perhaps as a result of an update to a data model  
far away), it only has to dereference a URL to discover a plain text  
list of utypes that the new one is 'like', and it can process the  
element as any one of those that it recognises, such as a previous  
version, or a very generic notion such as 'date'.  That doesn't  
require any updating on the part of the developer -- only some  
bookkeeping on the part of the organisation which has updated its data  
model and associated utypes.



I didn't see the beginning of this thread (and the archive at <http://www.ivoa.net/forum/dal/ 
 > only goes up to 21 April), but if utypes (already sitting above  
UCDs and still not even defined) are sufficiently incomplete that we  
require 'ctype' and 'xtype', too, then I think that has to be regarded  
as a defect of utypes.

All the best,

Norman


-- 
Norman Gray  :  http://nxg.me.uk
Dept Physics and Astronomy, University of Leicester