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Re: Placing a comment on a relationship?!

From: Adrian Walker <adrianw@snet.net>
Date: Thu, 20 May 2004 14:29:40 -0400
Message-Id: <>
To: Dan Brickley <danbri@w3.org>
Cc: Richard Lennox <listserve@richardlennox.net>, www-rdf-interest@w3.org

Hi Dan --

You make a good point of course (see below), but it does not solve the problem

The problem is that RDF/OWL is by design a machine-oriented notation, and 
one in which it is easy even for expert people to make mistakes when they 
try to code 'raw'.

For example, a now apparently defunct web site (interprise.com) last year 
gave an example that can be summarized as

     some-subject is related by rdf:type to some-subclass
     that-subclass is related by rdfs:subClassOf to some-object
     that-subject is related by rdf:type to that-object

The rule looks reasonable, and on the data that interprise supplied, its 
conclusions were in line with normal intuition**

However, if you plug in "Clyde", "elephant" and "species", you get " Clyde 
is related by rdf:type to species" .   So presumably, the rule is wrong as 
it stands.

Yet, we need a rule of this nature, so what to do?  It will not be enough 
to give a different rule at the machine-oriented level, because it also 
could be too easy to misunderstand.

A possible improvement is to label each predicate with an English sentence 
for human use, and tie the labels firmly to the underlying machine 
notation.  Consider***

   some-item is a member of the set some-set
   that-set is a named subset of the set some-superset
   that-item is a member of a named subset of that-superset

The conclusion is careful to only tell a human reader  that "Clyde is a 
member of a named subset of species".

Of course, simple examples like Clyde-elephant-species do not seem all that 
important at first sight.  However, if people can easily write a simple 
example to give an absurd conclusion, then we really do need to improve the 
situation for real-world tasks.

The above is one way of trying to improve things.  Perhaps there are others?

                                 Cheers,   -- Adrian

** You can run this example, called RDFreasoning1, by pointing a browser to 
www.reengineeringllc.com  and logging in to the "demo" ID

*** Likewise for ClydeElephant1

                                            INTERNET BUSINESS LOGIC


Dr. Adrian Walker
Reengineering LLC
PO Box 1412
CT 06011-1412 USA

Phone: USA 860 583 9677
Cell:    USA  860 830 2085
Fax:    USA  860 314 1029

At 10:44 AM 5/20/04 -0400, you wrote:
>* Adrian Walker <adrianw@snet.net> [2004-05-20 10:46-0400]
> >    Richard --
> >
> >    Actually, I think you may have put your finger on a general problem.....
> >
> >    The general problem is, deductions that seem OK in RDF-ish notation are
> >    sometimes OK in English, and sometimes absurd.
> >
> >    There's a nice example from John Sowa about this:  Clyde is an elephant,
> >    elephant is a species, therefore Clyde is a species.  That's wrong in
> >    English, but there are ways of writing it in RDF/OWL that look OK.
>This is a classic example, stemming from two senses of 'isa'. Modern KR
>systems including RDF/OWL distinguish them carefully. In RDF, we have
>'rdf:type' and 'rdfs:subClassOf' to represent two notions which
>might colloqially be described as 'is a' by an English speaker. In RDF,
>'type' relates an individual to a class; 'subClassOf' is a relation
>between classes.
Received on Thursday, 20 May 2004 14:43:44 UTC

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