utype questions

[Guy Rixon]

Roy,

your observation-time example is a excellent example of what utypes  
are good for.

all the tests in the conditional are guesses or approximations, except  
the one on utype. All will occasionally give false-positive matches  
except the utype test (OK, the UCD one might be reliable for this  
particular UCD).

Cheers,
Guy


On 12 May 2009, at 12:28, Roy Williams wrote:

> Fabulous job, Norman. You have crystallized many of my own unspoken  
> worries. And now there is a plan for a new attribute in VOTable with  
> yet another meaning.
>
> What is the VOTable parser to do? What I do is to in the metadata to  
> see if the table fits the data model I am looking for. Just like  
> looking in the FITS keywords for the ones we recognize.
>
> Here, for example, is some toy code from a VOTable application that  
> is expecting a time series, and is therefoe looking for the FIELD  
> which is the observation time:
>
>   if FIELD.ucd.containsString("time.epoch")
>   or  
> FIELD 
> .utype 
> .containsString("Spectrum.Char.TimeAxis.Coverage.Location.Value")
>   or FIELD.units.containsString("ISO8601")
>   or FIELD.representation.containsString("STC-S"):
>     print "Found FIELD with observation time"
>
> Roy
>
>
>
> Norman Gray wrote:
>>
>> Greetings, all.
>>
>> I am often confused about what utypes are and are for, and when I
>> talk to people who claim to be less confused, they give a variety of
>> very certain and confident answers, which are rarely compatible with
>> each other.  These incompatibilities are not merely differences of
>> opinion about syntax, but appear to represent fundamentally different
>> perceptions of how utypes are scoped and designed.
>>
>> I've collected a number of my puzzles about utypes into a single  
>> document, at
>>
>>    http://nxg.me.uk/note/2009/utype-questions/
>>
>> I don't think these are necessarily hard questions.  The problem is  
>> that some of them have multiple obvious answers, which are  
>> incompatible, and all of which I've heard represented as The  
>> Consensus.  I don't believe this is a secure basis on which to  
>> build a robust standard.
>>
>> I hope the questions are useful.
>>
>> All the best,
>>
>> Norman
>>
>>
>
> -- 
>
> California Institute of Technology
> 626 395 3670