[QUAR] Re: Expressing position in RDF

[Matthew Graham]

Hi,

I'm working on the data portfolios for VOEvents that some of you have  
heard me talk about (at Practical Semantic Astronomy 2008 and IVOA  
Trieste). Each VOEvent gets associated/translated into a XHTML/RDFa  
document that then gets added to as more data/information about the  
event becomes available. In this particular instance, I have the STC  
from the VOEvent which will generate an XHTML statement: "This object  
has RA= ... and Dec=..." but will also have the same information  
expressed in RDFa.

The portfolios get parsed and the RDF(a) put in a triple store or data  
discovery launched because some criteria are met, etc.

	Cheers,

	Matthew

On Oct 14, 2008, at 12:15 PM, Douglas Burke wrote:

>
> 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
>>>
>
>