[Developers] Cactus RDF: URIs

Thomas Radke tradke at aei.mpg.de
Thu Sep 7 11:56:17 CDT 2006

Erik Schnetter wrote:
> On Sep 7, 2006, at 11:03:11, Dylan Stark wrote:
>> Hi,
>>   I would like to find out what a good naming convention would be for
>> giving URIs to the different entities we will be collecting the
>> metadata on, such as thorns and parameters. I know that in the RDF we
>> can talk about the concept of "a thorn with a name", but it could be
>> beneficial to have a URI for that concept. An example might be
>>     http://www.cactuscode.org/thorn/WaveToy.
>> The statement "ParameterFile activates <http://.../WaveToy>" would be
>> equivalent to "ParameterFile activates the Thorn with name 'WaveToy'.
> In the past, people have copied thorns from one repository to  another, 
> creating two thorns with the name name.  While this is bad  practice, it 
> has happened and will probably happen again.  An  additional qualifier 
> is needed.
> Cactus already has the concept of arrangements.  What about
>     http://www.cactuscode.org/rdf/thorn/CactusWave/WaveToy
> instead?  The "rdf" part would make sure that it does not conflict  with 
> any web pages that people may create, and "CactusWave" is the  
> arrangement name.  So far, arrangement names have been unique.
> Of course, thorns change with time, so even that identifier does not  
> have a static meaning.

The entity (eg. 'WaveToy') that we actually want to describe is not some 
anonymous entity but a very concrete one, namely the one that's being 
used in a specific simulation. As Erik says, many Cactus users may use a 
thorn called "WaveToy" but each one could have a  different 
implementation; there are no thorn signatures to uniquely identify 
thorns. So the URI referencing that entity must somehow indicate that it 
belongs to a specific simulation.

Therefore we decided for the Cactus metadata management service 
developed in AstroGrid that the URI prefix (ie. the unique namespace for 
all metadata about that simulation) contains a unique simulation ID. 
After that prefix, all other metadata is listed, basically following the 
hierarchical structure you suggested (eg. "ThornList/<thorn>", 
"<thorn>/<parameter>", etc.).

Cheers, Thomas.

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