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RE: What do the ontologists want?

From: Peter Crowther <peter.crowther@networkinference.com>
Date: Tue, 15 May 2001 09:57:56 +0100
Message-ID: <B6F03FDBA149CA41B6E9EB8A329EB12D05A283@vault.melandra.net>
To: "'pat hayes'" <phayes@ai.uwf.edu>, Jonathan Borden <jborden@mediaone.net>
Cc: www-rdf-logic@w3.org
> From: pat hayes [mailto:phayes@ai.uwf.edu]
> [Jonathan Borden wrote:]
> > Certainly being able to quote statements/triples is useful 
> > ... indeed a practical requirement.
> Can you (or anyone) say why the ability to quote is considered a 
> practical necessity? From where I am standing it seems an arcane and 
> exotic ability, not one that is of central practical importance. What 
> is the practical utility of being able to refer to a predicate, 
> rather than use it?

I've got sympathies on both sides of this, based on past and present systems
I've used; summarised below.  I'm also pretty hard-nosed about why I'm doing
this; summarised in the last paragraph.

Some systems are more obvious to design if there is a facility to make a
statement about a statement.  Almost always, these are attributions: the
typical example seen on this list, and the examples we used in SMK, are of
the form "X says 'statement Y'".  (Question: Can anyone come up with a
different use for reification?  If this is the only special-case, should
there be a different mechanism for attribution?)

We were working with clinical systems, where the ability to attribute
particular statements to clinicians was of legal importance in case of
lawsuits.  No attribution, no adoption of system.  We chose to implement
this using reified triples; this opened up a can of worms as far as the
implementation was concerned, as we could then make statements about the
statements of attribution, and we could also construct self-referencing
systems such as:

		#2 writtenBy peter (triple ID #1)
		#1 writtenBy peter (triple ID #2)

Overall, the approach caused more problems than it solved; GRAIL and the
more recent work at the University of Manchester dropped this facility, and
we put in special-case code for dealing with attribution.

However, we were dealing with a knowledge base that was totally under our
control.  One of the interesting features of RDF is that it allows an author
to mark up a source over which they have no direct control; one view of
search engines and classifications like Yahoo! is that they will evolve into
huge metadata repositories rather than simply free-text engines.  In this
situation, there are a couple of areas that need thought:

1) How does a third party refer to portions of another's work?  Especially
if that work is RDF?  For example, I might want to say that I agree with all
the statements in a particular document except statements A, B and C.

2) (a) Should one be able to reason about such statements / does it gain us
anything; (b) How should one be able to reason about such statements if it
does gain us anything?

Apart from these areas, I agree with Pat: it is an arcane and exotic
ability.  It is also an ability that will cost us very dearly in terms of
being able to reason about the resulting (rather baroque) structures.

Ultimately, I'm building systems that people will use because they save time
and/or money.  Few standards have been adopted unless the standard has aided
this process, and I suspect RDF-Logic is no different.  Do these areas
introduce enough new functionality that results in savings in other areas,
that the design, implementation, run-time and human costs are worth it?  Or
is it more effective to solve a few specific problems in other ways?

		- Peter
Received on Tuesday, 15 May 2001 04:58:27 UTC

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