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Re: Social meaning discussion 6th March

From: by way of <bparsia@isis.unc.edu>
Date: Thu, 06 Mar 2003 05:38:48 -0500
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To: w3c-rdfcore-wg@w3.org

[stopped by subscriber rules -rrs]

Date: Wed, 5 Mar 2003 23:56:40 -0500 (EST)
Message-Id: <30C4A40F-4F90-11D7-9F85-0003939E0B44@isis.unc.edu>
Cc: Graham Klyne <GK@NineByNine.org>, Tim Berners-Lee <timbl@w3.org>,
    Dan Brickley <danbri@w3.org>, Brian McBride <bwm@hplb.hpl.hp.com>,
    RDF Core <w3c-rdfcore-wg@w3.org>
To: pat hayes <phayes@ai.uwf.edu>
From: Bijan Parsia <bparsia@isis.unc.edu>
In-Reply-To: <p05111b06ba8a8cf71a13@[]>
Message-Id: <30C4A40F-4F90-11D7-9F85-0003939E0B44@isis.unc.edu>
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Just a quick question.

While preparing for tomorrow's session, I found two passages of particular 
interest. The first is  section 2.2.3 of RDF Model and Syntax 
(http://www.w3.org/TR/REC-rdf-syntax/). I quote:

"""When we write a sentence in natural language we use words that are meant 
to convey a certain meaning. That meaning is crucial to understanding the 
statements and, in the case of applications of RDF, is crucial to 
establishing that the correct processing occurs as intended. It is crucial 
that both the writer and the reader of a statement understand the same 
meaning for the terms used, such as Creator, approvedBy, Copyright, etc. or 
confusion will result. In a medium of global scale such as the World Wide 
Web it is not sufficient to rely on shared cultural understanding of 
concepts such as "creatorship"; it pays to be as precise as possible.

You can think of a schema as a kind of dictionary. A schema defines the 
terms that will be used in RDF statements and gives specific meanings to 
them. A variety of schema forms can be used with RDF, including a specific 
form defined in a separate document [RDFSchema] that has some specific 
characteristics to help with automating tasks using RDF."""

The first paragraph seems  to express at least some of the concerns raised 
to justify section 4 (either the current version or newer ones). The second 
paragraph seems utterly false, and rather different than the way Tim is 
trying to fix "the meaning" of rdf graphs (though it has a related flavor).

So, 1) is most (or all) current RDF (problematically) meaningless, and 2) 
if so, what exactly is broken about the current situation?

(I want these to be rhetorically, but I guess I mean them quite seriously. 
I know what was wrong with the old BNF for the grammar (ambiguity) and how 
that broken things (different implementors made different, justifiable, 
incompatible choices). That has a straightforward fix, with clear benefits 
(i.e., serializers and parsers will produce compatible documents). I don't 
have the same sense for "the meaning problem", all i find is that the 
attempts to specify it all seem like non-starters in a variety of ways. And 
yet, RDF goes on :))

The second passage is section 1 of the last call working draft of  RDF 
Semantics (http://www.w3.org/TR/rdf-mt/), in particular section 1.3. I 
quote the second paragraph:

"""The following definition of an interpretation is couched in mathematical 
language, but what it amounts to intuitively is that an interpretation 
provides just enough information about a possible way the world might be - 
a 'possible world' - in order to fix the truth-value (true or false) of any 
ground RDF triple. It does this by specifying for each uriref, what it is 
supposed to be a name of; and also, if it is used to indicate a property, 
what values that property has for each thing in the universe; and if it 
used to indicate a datatype, we assume that the datatype defines a mapping 
between lexical forms and datatype values. This is just enough information 
to fix the truth-value of any ground triple, and hence any ground RDF 
graph. (We will show how to determine the truth-values of non-ground graphs 
in the following section.) Notice that if we left any of this information 
out, it would be possible for some well-formed triple to be left without a 
determinate value; and also that any other information - such as the exact 
nature of the things in the universe - would, regardless of its intrinsic 
interest, be irrelevant to the actual truth-values of any triple."""

I'm having trouble seeing why this passage (plus the relevant other bits) 
doesn't say pretty much all you want and need to say *in the RDF specs* 
about the "determinate" (yeek!) meaning of  RDF (and, actually, thus about 
the "effective" meaning). Indeed, this section even captures a bit of the 
"let's obsess about predicates" and definitions line (in so far as I can 
make it out :)):

"""In other words, an assertion amounts to stating a constraint on the 
possible ways the world might be. Notice that there is no presumption here 
that any assertion contains enough information to specify a single unique 
interpretation. It is usually impossible to assert enough in any language 
to completely constrain the interpretations to a single possible world, so 
there is no such thing as 'the' unique RDF interpretation. In general, the 
larger an RDF graph is - the more it says about the world - then the 
smaller the set of interpretations that an assertion of the graph allows to 
be true - the fewer the ways the world could be, while making the asserted 
graph true of it."""

If the point of Tim's earlier email is that the RDF specs need to say 
something like: "use natural language (such as English) to supply enough 
information to sufficiently constrain the interpretations to a single 
possible world, preferably the actual world", well, ok, but that no one 
will do this, usually because one just isn't able. (The "ground it in 
English" example isn't going to cut it, even with a simple case like 
'uncle'. No sibling of mind has (yet) had a child, yet I've been called 
"uncle", and, I think, not all that deviantly.)

Bijan Parsia.
Received on Thursday, 6 March 2003 05:38:45 UTC

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