[QUAR] Re: Expressing position in RDF

[Rob Seaman]

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