Expressing position in RDF

[Ed Shaya]

"Let a hundred flowers blossom"  -- Mao

In a certain context I might actually say, "HDNNNN has RA 13.53" and 
totally leave out epoch, equinox, system, units, and error and it would 
be useful.  In a peer reviewed journal, I would not think of saying this 
unless  all  those  metadata are  clearly tied down.  So, most of the 
discussion on this thread today is not a discussion of OWL/semantics but 
rather of astronomical contexts and purposes.  We hit these same 
sticking points in STC and in DM.  The beauty of OWL/semantics is the 
openness that allows it to grow until it becomes completely parallel to 
normal language so you can provide whatever is appropriate for the given 
context.  The downside, besides sheer size,  is some 
noninteroperability.   The VOEVENT software might prefer  "MDNNNN  
a:hasRA  13.53^^float",  and that is fine. But, a  more elaborate 
analysis package  might simply not accept such statements.  With some  
intense coding, it may  understand that this statement sets an RA in 
some equatorial system at some epoch, and it will either set these as 
unknowns or put out a request for additional information. 

This may be a heretical statement, but complete interoperability may not 
be the best course.

Ed


Bernard Vatant wrote:
> Hi all
>
> Have been lurking at this conversation so far. Some thoughts below, 
> about this very generic use case in science : how do you attach 
> measurement results to an object? Seems to me the scientific community 
> (at least its members involved in Semantic Web) should try and 
> standardize this at some point. 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. 
> Of course hoping astronomers would be leaders in such a process :-)
>
> Matthew wrote
>> Although this works, it is very verbose for such a simple (!) 
>> statement. To sell this sort of stuff to end users, we really need a 
>> practical and succinct set of object properties that would allow me 
>> just to do:
>>
>> :MyObject a:rightAscension 134.556^^xsd:float
> Two remarks
>
> 1 : "object properties" might be confusing in this conversation 
> context. I guess you mean "properties of objects", not 
> "ObjectProperty" in the OWL sense ... since actually your 
> a:rightAscension would be a datatype property.  
> 2 : With such shortcuts, you don't assert the coordinate reference 
> J2000 and the unit, so it is implicit, which is not a good idea ... or 
> you have to built-in the coordinate system and unit in the property ...
> :MyObject a:rightAscensionJ2000In DecimalDegrees 134.556^^xsd:float
>
> The problem with this is that it leads to a proliferation of 
> properties, and you can't in this case assert "properties of the 
> property", such as accuracy of the value, method of acquisition, and 
> whatever relevant description of the measure process ... Direct 
> assertion is blurring the fact that attaching a property-value pair to 
> an object, in science, is called a measurement, of which description 
> must come along with the data if those data want to be qualified as 
> scientific data.
> So it is not only a technical issue of representation, what is at 
> stake is what qualifies scientic data from simple property-value 
> pairs. I don't know which "end users" you have in mind, but there is a 
> huge trend in science outreach to hide all the data context to 
> "simplify" the presentation of data. See what I mean :-)
>
> This is the local illustration of all the issues debated at length in 
> the Semantic Web community at large about trust, data quality etc.
>
> Ed, for a simpler expression of your example, one can use nested blank 
> nodes for coordinates (it's indeed a typical use case of blank nodes)
> and I don't think either asserting the class of those nodes is really 
> useful, nor specifying a URI. Merging or matching of such information 
> would in any case drill down to the values. OTOH, I added the 
> precision of the data, and some Dublin Core metadata on the 
> measurement. Which is not possible to add using the direct property on 
> the object.
>
> :MyStar a a:star;
> ivoa:hasPosition _:b1
>
> _:b1 geo:hasCoordinate _:myRA.
> _:b1 dc:source   :MyCatalog
> _:b1 dc:date   "2008-10-14:00.00"
>
> _:myRA a a:rightAscension;
>  q:hasFloat 34.5343^^xsd:float;
>  q:hasUnits ui:degree;
>  q:hasPrecision  0.0002^^xsd:float.
>
> My 0.02

You left out _:b1 a J2000Coordinates.

> Bernard
>
>>>
>>> On Oct 13, 2008, at 7:24 PM, Ed Shaya wrote:
>>>
>>>> Here is "MyStar has a J2000 RA of 34.5343 degrees, it would be 
>>>> something like this in N3:
>>>>
>>>> :MyStar a a:star;
>>>>    ivoa:hasPosition :MyCoordinates.
>>>>
>>>> :MyCoordinates a 
>>>> a:J2000Coordinates;                                                       
>>>> geo:hasCoordinate :myRA.
>>>>
>>>> :MyRA a a:rightAscension;
>>>>   q:hasFloat 34.5343^^xsd:float;
>>>>   q:hasUnits ui:degree.
>
>