No universal things Re: comparing XML and RDF data models

>> [Bijan] I don't know what a universal thing (is).
>>     
>
> [Peter] Sorry, I thought that would be obvious. In my realist view there are
> things that people are trying to describe using RDF and those things
> have identities, which we are labelling with names, or describing
> through identifying properties. These are universal things. If you
> want to establish equality you are likely to be doing it at this
> level, unless you assume that markup is everything and a thing is only
> in existence because there is a description of it, and the description
> of the thing causes the thing to exist.
>   
Peter, sorry to be as harsh on that as Bijan has been, but I consider 
this viewpoint as not sustainable, and dangerously naive.

I for one assume very strongly indeed that 'the description of the thing 
causes the thing to exist', and my hunch is that Bijan will follow me on 
this (at least I hope so). What we deal with in our information systems 
are only descriptions (signs). A 'thing' exists insofar as we have made 
a description which somehow cuts out the world representation in some 
arbitrary way between 'this thing' and the rest. The world is a 
continuum, it's not naturally divided into things which would be given, 
and  which we could describe as accurately as possible. Things emerge 
from descriptions, conversation about descriptions, and so do identity 
and difference. We might at some level of granularity agree we are 
describing the 'same' thing, based on the mutual logical consistency of 
descriptions, and a mutual agreement on which set of property/value 
pairs we consider as "identifying". Then further down the road, drilling 
down more precisely our respective descriptions, we can come to a point 
were those descriptions are no more consistent, and we then agree we 
were speaking about different things indeed. This should not be an 
issue, but the basis of day-to-day practice.
I had this viewpoint even before beginning to work in those 
technologies, and was quite happy to find out that ten years or so of 
work in very various industries and projects had brought me a huge pile 
of examples to illustrate and confort it. Not only I don't know what a 
universal thing is, but I'm pretty much convinced that this is a void 
and useless concept. It's been counter-productive in science for 
centuries. Physics had to go over the notion of universal thing to 
understand that light is neither a wave, nor a particle. Biology to go 
over the notion of taxa as rigid concepts based on phenotypes to 
understand genetics etc. Many examples can be found in all science domains.
My day-to-day experience in ontology building, listening to domain 
experts, is indeed not that 'there are things that people are trying to 
describe', but that 'there are descriptions people take for granted they 
represent things before you ask, but really don't know exactly what 
those things are when you make them look closely'. When you play the 
game, simply asking questions such as "in which way X is different of 
Y", or "what does this mean exactly", you always bring domain experts to 
acknowledge this. And all our job is not to figure out 'what the domain 
things really are' and 'describe them properly', but to bring people to 
acknowledge the arbitrary nature of their descriptions, the fundamental 
impossibility to capture their referent in an exhaustive way, hence the 
necessity of consensus at a certain level of complexity and granularity, 
on which to build systems that work. The world does not need to be 
consistent and logically organized, but our systems need to be.

Bernard

-- 

*Bernard Vatant
*Knowledge Engineering
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Received on Thursday, 3 July 2008 09:53:23 UTC