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Re: Meaning of URIRefs

From: Peter F. Patel-Schneider <pfps@research.bell-labs.com>
Date: Fri, 25 Oct 2002 16:03:27 -0400 (EDT)
Message-Id: <20021025.160327.60861024.pfps@research.bell-labs.com>
To: sandro@w3.org
Cc: phayes@ai.uwf.edu, www-rdf-interest@w3.org

From: Sandro Hawke <sandro@w3.org>
Subject: Re: Meaning of URIRefs 
Date: Fri, 25 Oct 2002 15:11:49 -0400

> > >The way around these problems is to split definitional content and
> > >general content into different documents.
> > 
> > The trouble with this kind of reply is that it requires all web users 
> > to obey unspoken and hard-to-define rules of good behavior.  Note 
> > that you, Sandro, were at pains to explain in your earlier message 
> > that 'definitional' didn't have any sharp meaning. A very good point; 
> > but then it is hardly reasonable to immediately require that all web 
> > users segregate their content into documents according to whether or 
> > not they satisfy this meaningless distinction.
> >
> > BUt more seriously, we can SAY things like this all we want, but 
> > people will not in fact do it. Are you going to try to tell, say, 
> > Nokia, that they must segregate all their RDF content into different 
> > documents according to whether or not they are considered 
> > 'definitional'? They would (correctly) laugh at you.
> 
> (There's some lag in this message chain, so perhaps I've already
> addressed this to your satisfaction.  But I'll err on the verbose
> side.)
> 
> I can suggest to Nokia that if they segregate their data carefully,
> they will be facilitating use and reuse of the data.  It's not unlike
> HTML web sites, where there is ongoing tension between
> lazy/short-sited design and good design, where good design has all
> sort of benefits which may not be immediately obvious.


> The segregation into definitional and non-definitional triples is
> certainly an art, but perhaps it's not as black as it seems.  DAML
> users don't seem to have much trouble distinguishing between ontologies
> and instance data.  

The distinction between ontologies and instance data is very different from
the definitional vs non-definitional distinction.  In any case, drawing the
line between ontologies and instance data is not easy at all.

> I haven't seen a lot of URIRefs pointing into
> instance data from other instance data, and I'm not sure what exactly
> people intend when they do that.  

Well, all my examples about George-Bush-the-lesser require the use of a
well-known identifier for that George Bush.  It sure seems to me that these
are all examples of pointers from instance data to other instance data.
Just about any appliction of the semantic web that I can think of, from
travel planning to phone routing to fully automated assistants, require a
network of instance data on multiple sites with many references betwee
them.

> Does someone have some real uses cases where this segregation does NOT
> seem like good information architecture?  

Which segregation?  It certainly does not always make sense to require that
ontologies do not contain any instance data.  To pick a slightly outdated
example, how can you refer to ``friends of Bill'' without mentioning Bill
Clinton?  Yet ``friends of Bill'' sure seems ontological to me, and,
although this claim might be disputed by many in the far right, Bill
Clinton is an individual, not a class or category.

It also is extraordinarily difficult to make a distinction between
definitional and non-definitional information.  For example, it is
definitional that tigers are mammals?  It is definitional that tigers come
from India?  It is definitional that tigers are an endangered species?  It
is definitional that tigers are a symbol of royalty?  Is it definitional
that tigers are to be revered?  Is it definitional that Tigger is a tiger?

> Note that in many cases it's
> completely arbitrary in authoring RDF whether, when you say
>    
>      rdf:about="&foo;bar"
> 
> the &foo; entity is the document's own URI.  (If it is, it's the same
> as rdf:ID, give or take a hash mark.)  People often do it because
> they're not sure what else the foo might point to.  If they make this
> segregation, it would become clear.  &foo; is the definitional
> document.  Make it empty if you really have nothing definitional to
> say, but you can probably come up with something useful.
> 
>    -- sandro

Peter F. Patel-Schneider
Bell Labs Research
Received on Friday, 25 October 2002 16:03:37 GMT

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