[QUAR] Re: Expressing position in RDF

[Douglas Burke]

Matthew,

Perhaps if you can place your request in a broader context - I'm 
thinking along the lines of

   a) what system is going to create these statements about coordinates
   b) what system is going to use them

- so that we might begin to agree on what is simple for this particular 
task. Actually, I doubt we'd get that far, but I'd be interested to know 
what you're actually trying to do by "sematicising" positions ;-)

Doug


Matthew Graham wrote:
> Hi,
> 
> I'm happy for the philosophical discussion but am also trying to figure 
> out how to actually do something empirical. I can see exactly the same 
> arguments that we had about using STC in VOEvent applying to 
> representing positions in RDF. The 90:10 rule should apply and whilst it 
> is wonderful that I can describe any position in any coordinate system 
> using ontology X, why can't we have ontology Y that is small and simple 
> (that word again):
> 
> :myStar stc:UTC-TOPO-FK5#RA 134.56
> 
>     Cheers,
> 
>     Matthew
> 
> On Oct 14, 2008, at 11:47 AM, Rob Seaman wrote:
> 
>> Bernard Vatant wrote:
>>
>>> how do you attach measurement results to an object?
>>
>> This is begging the question in an observational science.  The 
>> existence of the object is the null hypothesis you're trying to test.  
>> Anyway, I don't think Matthew was looking for a philosophical 
>> discussion :-)
>>
>> But if you did want to pursue this, one might suggest starting with 
>> the distinction between the dependent and independent variables of the 
>> observation/measurement.
>>
>>> Seems to me the scientific community (at least its members involved 
>>> in Semantic Web) should try and standardize this at some point.
>>
>> This is the center of the scientific maelstrom.  One might have better 
>> luck first looking elsewhere.
>>
>>> I've been looking for relevant pointers to people working on this in 
>>> other domains (say e.g., Biology, Earth sciences ...) without much 
>>> success so far I'm afraid.
>>
>> Returning to the question at hand, this is an interesting point.  We 
>> act as if astronomical coordinates are particularly difficult.  They 
>> are, in fact, particularly well behaved.  Things tend to stay put on 
>> the celestial sphere (for many purposes).  Imagine building the same 
>> assertions for - say - wildlife management.  A herd of caribou doesn't 
>> stand still.
>>
>> One may, however, make assertions - as with stars - about the 
>> temperature of a particular caribou or other parameters such as sex or 
>> mass or age.  These are assertions inherent in the object itself.  One 
>> may make assertions about group behavior - a "cluster" of caribou.  
>> One may make assertions about evolutionary descent.
>>
>> But it is orders of magnitude more difficult to specify location 
>> (longitude and latitude as a function of time) for caribou than it is 
>> for stars.  And in astronomy, one is typically expressing targeting 
>> coordinates (explictly or implicitly) for future observations.  On the 
>> other hand, predicting the future migrations of caribou is simply 
>> impossible.
>>
>> It seems unremarkable to me that an assertion in an astronomical 
>> context (say, stars), might look something like:
>>
>>     X is a star
>>     X corresponds to target Y
>>     Y has WCS Z
>>     Z has an RA (along with a bunch of other attributes) - and 
>> corresponding to some fiducial point like the centroid of a PSF
>>
>> Compare to:
>>
>>     A is a caribou
>>     A is somewhere in Alaska
>>     Alaska has (complex and idiosyncratic) GIS data structure B
>>     B has a footprint the size of the lower 48 east of the Mississippi
>>
>> Rob
>>