[nvo-techwg] Referencing in XML for the IVO

[Paul Harrison]

Arnold Rots wrote:
> Appended is something that will work (and that I showed at the team
> meeting in abbreviated form).  It has URLs instead of IVO identifiers
> but that's a detail.
> 


I am not convinced that it is "just a detail" - I think that it is a 
crucial detail if we are to have any hope of standard xml tools being 
able to interpret such documents.

The ivo: scheme is an URI, so a registry must be used to actually locate 
the document, which is a two stage process, as the ivo: URI first gets 
resolved into an xml instance conforming to the Registry schema, which 
in itself contains a link to the URL of the xml instance fragment 
conforming to the STC schema. This double indirection should really be 
expressed in the source xml document - possibly with the help of 
Xpointer (http://www.w3.org/TR/2002/PR-xptr-framework-20021113/)

Having said all this, Xlink and Xpointer do seem to have stalled in 
developement somewhat - there seem to be few (if any) general 
implementations - possibly because once you allow more complex semantics 
for a link than simply "go there" it is difficult to build a general engine.


> Roy Williams wrote:
> 
>>Arnold
>>
>>Please excuse me, my schema expertise is not as good as yours, so I 
>>attempt to sketch some examples.
>>
>>What I want is to say, for example:
>><AstroCoordSystem
>>	ID="FK5-UTC-TOPO"
>>	xlink:href="ivo://stc.ivoa.net/FK5-UTC-TOPO">
>>so that any of the VO registries can tell me where to find the precise 
>>definition of this coordinate system, should that be required.
>>
>>Another example would be for observatory location. I would want to say:
>><ObservatoryLocation
>>	ID="Palomar"
>>	xlink:href="ivo://nvo.caltech.edu/observatories/Palomar">
>>
>>Is this what you envision?
>>Roy
>>
>>California Institute of Technology
>>626 395 3670
>>
> 
> --------------------------------------------------------------------------
> Arnold H. Rots                                Chandra X-ray Science Center
> Smithsonian Astrophysical Observatory                tel:  +1 617 496 7701
> 60 Garden Street, MS 67                              fax:  +1 617 495 7356
> Cambridge, MA 02138                             arots at head.cfa.harvard.edu
> USA                                     http://hea-www.harvard.edu/~arots/
> --------------------------------------------------------------------------
> 
> <?xml version="1.0" encoding="UTF-8"?>
> <ObsDataLocation xmlns="http://www.ivoa.net/xml/STC/stc-v1.23.xsd"
>     xmlns:crd="http://www.ivoa.net/xml/STC/STCcoords/v1.23"
>     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
>     xmlns:xlink="http://www.w3.org/1999/xlink"
>     xsi:schemaLocation="http://www.ivoa.net/xml/STC/stc-v1.23.xsd
>     http://hea-www.harvard.edu/~arots/nvometa/v1.23/stc-v1.23.xsd">
> 
>   <ObservatoryLocation id="MyObservatory" xlink:type="simple"
>        xlink:href="http://www.ivoa.net/xml/STC/STClib/Observatories.xml#MyObservatory"/>
> 
>   <ObservationLocation>
>     <AstroCoordSystem id="UTC-FK5-TOPO" xlink:type="simple"
>        xlink:href="http://www.ivoa.net/xml/STC/STClib/AstroCoordSystems.xml#UTC-FK5-TOPO"/>
>     <crd:AstroCoords coord_system_id="UTC-FK5-TOPO">
>       <crd:Time unit="s">
>         <crd:TimeInstant>
>           <crd:ISOTime>2005-04-15T23:59:59</crd:ISOTime>
>         </crd:TimeInstant>
>         <crd:Error>2</crd:Error>
>       </crd:Time>
>       <crd:Position2D unit="deg">
>         <crd:Value2>141 69</crd:Value2>
>         <crd:Error2Radius>0.05</crd:Error2Radius>
>       </crd:Position2D>
>     </crd:AstroCoords>
>   </ObservationLocation>
> </ObsDataLocation>
> 


-- 
Paul Harrison
ESO Garching
www.eso.org