Expressing position in RDF

[Matthew Graham]

Hi,

RDF is just like XML so questions of production, presentation and  
storage are really quite secondary. It's the representation of  
information that is the primary concern and the issue here is does the  
IVOA have a succinct way of representing celestial positions in RDF.  
As Ed, I think, said, RDF and ontologies are supposed to remove the  
need for context to provide meaning to the information and so how the  
RDF statement is used is also quite secondary. The statement means  
what it says whatever.

SPARQL is the query language for RDF and is very SQL-like so an  
inequality is just a constraint on the search predicate. The exact  
syntax is dependent on how verbose the RA expression is.

I would not use a SPARQL query to do intersections, though - we have  
STC and Footprint Services for that. There might an RDF statement that  
a data object has a footprint associated with it and but then the  
object will the URI for the footprint itself.

	Cheers,

	Matthew


On Oct 14, 2008, at 7:35 PM, Roy Williams wrote:

> Matthew
>
> I like Doug's question, asking how the RDF will be used: produced,  
> presented, stored etc. Another question in the same genre asks what  
> *queries* will run against this knowledge base. I suspect that "RA"  
> will be used in an arithmetical inequality -- "Give me all sources  
> with RA>240.0", also as part of a cone search or polygon. Is it  
> Sparql, the query language for RDF? How would an inequality be  
> framed as part of a Sparql query?
>
> More abstract, we could utilize RDF at a higher level -- not details  
> of coordinate systems, as in this naked quantity "RA". How about the  
> RDF handles "Regions" (of spacetime). With Regions, the questions  
> are no longer arithmetical, but rather boolean choices, about  
> intersection: "Does the Region in which this event lies intersect  
> with the spacetime coverage Region of the Catalina Survey?"
>
> Roy
>
>
> -- 
>
> California Institute of Technology
> 626 395 3670
>