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Re: How does RDF/OWL formalism relate to meanings?

From: Thomas B. Passin <tpassin@comcast.net>
Date: Wed, 07 Apr 2004 19:26:58 -0400
Message-ID: <40748E42.3040805@comcast.net>
To: public-sw-meaning@w3c.org

John Black wrote:

> ... You haven't mentioned resources, URIs, or the identification of the 
> former by the later.  Is that involved?  So far, it seems that you  
> only need the main URI to hang the owl:FunctionalProperty elements on,
> since the meaning is actually created by the addition of functional 
> properties.  Turning the question around, how does the URI/Resources 
> formalism relate to these meanings?  It would seem that the main 
> URI was almost irrelevant, you could substitute one for another 
> and, due to the functional properties, the meaning would be the same.
> Is this right?  How about the notion of the strength of one of my 
> employees.  Are there functional properties I can use to get a URI 
> to communicate to my audience that one of my employees is really 
> strong?  How do I make a URI stand for my notion of strength, so 
> that I can be sure my audience gets it?

It seems to me that you are conflating several different things -

1) Conveying something to a human audience.
2) The machine-understandable "meaning" of some block of RDF/OWL/whatever.
3) The "meaning" of URIs, and
4) The "meaning" of a resource.

These are not totally unrelated, but they are not the same, either.  Pat 
Hayes (for one) has been telling you this.

For human consumption, there are several primary ways to convey the 
intended "meaning" of some particular URI - remembering that a URI 
stands in some way for a "resource", which in turn may be retrievable 
over a network or not, and may be abstract or not.

The most straightforward way is to attach NL labels to the things in the 
RDF graph.  People read the labels and get some sense out of them.  They 
see and read the relationships and get some sense out of them.  Note 
that this process is very different from a process of precise 
communication between machines or autonomous agents.

Another thing that is done is to have the URI for a resource point to 
some readable text about the intended "meaning" (or at least identity) 
of the URI.  There is some ongoing debate about how to make that work, 
bearing in mind that the URI in question may or may not intend to 
identify the actual web page that would be retrieved by dereferencing it.

Next up the ladder would be to arrange for RDF to be received upon 
dereferencing the URI of a resource.  The RDF (possibly with some OWL, 
which of course is also RDF) would be more precise than text, but this 
may or may not help a person grasp the ideas better.

Another step is to identify a resource by identifying properties - that 
might be an inverse functional property, but not necessarily.  This is 
like saying "the man standing next to my car" - this does not describe 
an inverse functional property but may nevertheless be all that is 
needed.  Typically, several such properties would be used together to 
help identify the resource (which may represent a concept or a term in a 
vocabulary) in question.

Remember that, to computers, it is all bits, that is to say, symbols. 
So the whole ball of wax - Semantic Web-wise - is pretty much a bunch of 
abstract symbols and rules for their manipulation.  That is like 
Newton's laws, for example.  They can be studied in an abstract 
mathematical way as symbol manipulation, or they can be studied from a 
point of view grounded in the motion of real things that have mass.  The 
only way you are going to get a computer so grounded is to have its 
results and its inputs be somehow appropriately interact with the real 
world.  And getting that to happen is something ouside of the realm of 
abstract symbol manipulation.

So you want your "audience" to grasp your notion of "strength"?  Then 
tell them what it is, tell them that the URI 
http://www.example.org/ontology/strength has a lable "John Black's 
notion of Strength".  Point them to some online text that explains it. 
Just don't expect an RDF processor to magically know to make all those 
inferences that you hope your audience would.

What about OWL? Well, with neither RDF nor with OWL can you say that "no 
man can have an arm strength of more than 500 kg", just to make a crude 
example here.  But with OWL, you can restrict - in a standard way that 
an OWL processor would honor - the allowed values of properties (to some 
degree), including the "John Black's Strength" property.  That may 
accomplish enough of what you want to be worth doing.

I realize that this post was long.  Does it start to address some of 
your questions?

Cheers,

Tom P
Received on Wednesday, 7 April 2004 19:23:25 GMT

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