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[Rob Seaman]

Norman Gray wrote:

>> Wouldn't it be better for me to say that the thing is a http://blah/2008#X 
>>  once and for all?  At least then I'm committing myself to what  
>> this concept means in 2008, and not whatever shades of meaning it  
>> might acquire in the future.

Yes.  I think this is a requirement...however:

Bernard Vatant wrote:

> Sure enough. But what happens to applications relying on this URI,  
> but wanting to use only up-to-date versions of the concept. How will  
> they know when, if, how to ... update to new URIs and descriptions?

I suggest that there should also be a "latest" link that is redirected  
as appropriate.  At any given time there will be several historical  
versions, a single current version, and a single version under  
development.  Presumably each vocabulary will contain metadata  
describing versioning such that an application that cares about such  
changes can detect them.  Beyond that we start to enter a realm of  
evolutionary complications that I don't think we're ready to deal with.

For instance, Bernard waxed poetic on several aspects of the evolution  
of meaning:

> Indeed. This is a very difficult question. What does "meaning the  
> same thing" mean exactly? Formally a concept is defined by its  
> description. The description changes with time. At which point is a  
> concept different? etc. As said by others, dc concepts might be more  
> stable than astronomy concepts.

> Just thinking aloud. I have several ongoing projects dealing with  
> evolution of concepts. For example we've started discussing that at  
> geonames.org. Geographical  are like concepts, they are created,  
> named, renamed, merged, destroyed etc ...
>>

> Deprecation mechanism can be implemented in structured vocabularies.  
> Actually we manage that in Mondeca's software. You can't delete an  
> indexing concept without redirecting to another one. It does solve  
> every problem, for example it does not provide any solution to the  
> situation where a single concept is split into several ones, etc.
>>

> Concepts, like reference systems, have a certain level of stability.  
> Otherwise language and science would be impossible :))
>>

> "Operations on concepts", so to speak, seem to be out of the  
> specification - as far as I understand. Look closely at the last  
> working draft, and, as said above, feel free to feedback on the SKOS  
> forum. Now is the moment to speak, before the specification is cast  
> in stone.

These difficult questions are ultimately the heart of the exercise.   
The point of science is to explore and describe new realms of  
understanding.  This is certainly true of VOEvent, but also of the VO  
in general.  Each new contribution to the literature is precisely a  
refinement or challenge to prior understanding, often including  
changes to the meaning of terms, classifications, identifications.  It  
is outside the scope of the vocabulary project itself to address this  
need, but our vocabularies must support mechanisms for polishing the  
comparative definitions on a continuing basis.  (Presumably the whole  
ontological "thang" is where the rubber will meet the road - well  
versioned vocabularies will support this later effort.)

In short - nothing means the same thing.  Nuance is everything.

Rob Seaman

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