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Re: Social meaning discussion 6th March

From: Dan Brickley <danbri@w3.org>
Date: Fri, 28 Feb 2003 20:34:20 -0500
To: Tim Berners-Lee <timbl@w3.org>
Cc: Brian McBride <bwm@hplb.hpl.hp.com>, Jeremy Carroll <jjc@hplb.hpl.hp.com>, pat hayes <phayes@ai.uwf.edu>, Bijan Parsia <bparsia@isis.unc.edu>, Graham Klyne <GK@ninebynine.org>, RDF Core <w3c-rdfcore-wg@w3.org>
Message-ID: <20030301013419.GM24319@tux.w3.org>

* Tim Berners-Lee <timbl@w3.org> [2003-02-28 15:34-0500]
> Dan Brickley wrote:
> 
> >* Tim Berners-Lee <timbl@w3.org> [2003-02-28 11:47-0500]
> > 
> >
> >>I am concerned that you have thrown out the baby with the bathwater.
> >>And still left some bathwater. ;-)
> >>Our views do seem rather different
> >>
> >>What is required, and easy, is to say what an RDF document means.
> >>
> >>What is not required and a bad idea is to explain how to use it.
> >>
> >>1. The meaning of an RDF document is that of the statements.
> >>2. The meaning of the statement is defined by the definition
> >>of the predicate, as applying to the subject and object identified by the
> >>definition of the subject and object terms.
> >>   
> >>
> >
> >This for me is the crux: do we mean the machine oriented 'definition'
> >in RDFS or OWL or N3, or some more rounded/scruffy/social notion of 
> >definition.
> > 
> >
> Whatever is available.  It tends to depend on the term.

Yes, there are a variety of strategies for representing the meaning of a 
term. The RDFS spec tries to acknowledge this in 
http://www.w3.org/TR/rdf-schema/#ch_comment where we say:
	"""A variety of documentation forms can be combined to indicate 
	the intended meaning of the classes and properties described 
	in an RDF vocabulary. Since RDF vocabularies are expressed 
	as RDF graphs, vocabularies defined in other namespaces 
	may be used to provide richer documentation."""
(I suspect we could usefully lose the word 'intended' there; 
 and I certainly wouldn't replace it with 'social'!)

 
> >Use case: I want to add 'foaf:uncle' to my FOAF vocabulary at 
> >http://xmlns.com/foaf/0.1/ and intend to express as much of the 
> >conventional
> >meaning of 'uncle' as I can with the technology available, ie. RDFS + 
> >OWL + N3 + HTML/prose. In the case of 'uncle', most of the meaning is 
> >invisible
> >to RDF/S and OWL. But most of it could be handled by N3 rules, assuming 
> >we had foaf:parent, foaf:sibling, gender vocab etc.
> > 
> >
> Well, that is a big assumption.    So let's be sepcific
> 
> { ?x :uncle ?y } log:iff  {  ?x   :parent  [  :brother ?y ] }.

(OK, lets forget the 'husband of aunt' case for simplicity.)
> 
> is a precise definition of the term for someone for whom parent and brother
> are defined.  But this of course doesn't really help us as somewhere the
> thing has to be grounded in english.
> 
> '"?x :uncle ?y" indicates that y is the uncle of x'
> 
> is an english definitoin which will do for a lot of people.

Yes, though I do hope at some point a WG offers some best practice 
guidelines to authors of rdfs:comment or owl2:comment properties to 
help them write their comments in such a way. Imagine if they wrote
"'xyz(?x,?y)' indicates that there is an xyz relation between ?x and ?y".
Or variations on that theme. We can I think do an incrementally better 
job of helping people be clear about the meaning of the terms they create.

This view requires that we conceive of the possibility of there being a 
gap between term meaning and what definition_s_ of the term say, especially
as there may be various definitions, and these may be refined and 
improved over time. The convenient idealisation is that there is a 
single meaning towards which all these definitions are fumbling...

> I would expect a good spec to have both.

I very much agree. Belt and braces. HTML, RDFS, OWL, (rules, ..., ...).

> The formal  information is a useful axiom.

Yes. And I believe many of us anticipate there being languages in 2-3 
years time that will make such formal information more widely accessible
within RDFS/OWL/+++ vocabulary descriptions. 
 
> >So when you say 'the definition of the predicate', that to me is where 
> >our problem lies. (I'm happy btw having predicates drive the meaning 
> >of statements, though I think this is something we stipulate rather than 
> >show). Which 'definition' of the predicate sets the meaning?

> One would expect that any maths given with an english definition would be
> consistent with it.

A reasonable expectation, and one that indicates something we've not 
really explicitly articulated: that we (well, maybe 'we') believe 
as our guiding fiction that class and property terms have a meaning 
that is independent of the languages (html, rdfs, owl, n3, ...) that 
we use to try to characterise that meaning. When all goes well, 
those varying characterisations are in sync. When things go badly (discuss...:)


This is somewhat related to RDF's practice of treating properties 
and classes as just more entities from the domain of discourse: they have a 
life beyond the RDFS assertions that describe them, or the OWL-encoded 
rules that describe them slightly better. There are, to stick with 
my use case above, facts of the matter about the proper use of 
the 'foaf:uncle' which we attempt to capture using whatever tools are 
within our grasp. Meanwhile, the property gets deployed and used. This 
division of labour allows people to get out there and _use_ RDF 
while W3C WGs work on better ways (OWL being the latest but I doubt 
the final) of characterising the meaning of these terms.

Dan

> Tim
Received on Friday, 28 February 2003 20:36:28 EST

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