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Re: help wanted: RDF issue rdfms-assertion

From: patrick hayes <phayes@ai.uwf.edu>
Date: Wed, 29 May 2002 14:43:19 -0500
Message-Id: <p05111728b91ad019f95a@[]>
To: "Tim Berners-Lee" <timbl@w3.org>
Cc: "Brian McBride" <bwm@hplb.hpl.hp.com>, w3c-rdfcore-wg@w3.org

>----- Original Message -----
>From: "Brian McBride" <bwm@hplb.hpl.hp.com>
>To: <timbl@w3.org>
>Cc: "RDF Core" <w3c-rdfcore-wg@w3.org>
>Sent: Tuesday, March 26, 2002 1:38 PM
>Subject: help wanted: RDF issue rdfms-assertion
>>  Tim,
>>  The RDFCore WG seeks your help with an RDF issue, rdfms-assertion:
>>     http://www.w3.org/2000/03/rdf-tracking/#rdfms-assertion
>>  [[
>>  Summary: RDF is not just a data model. The RDF specs should define a
>>  semantics so that an RDF statement on the web is interpreted as an
>>  assertion of that statement such that its author would be responsible in
>>  law as if it had been published in, say, a newspaper.
>>  ]]
>>  The WG believes that this issue originates with you.
>>  I would like to clearly establish what it is that you would like from us.
>>  A number of concerns have been raised about this issue:
>>     o RDF is just one of several specifications that are 'in play' when an
>>  RDF statement is retrieved from the web.  What is the minimum the RDF
>>  must say to achieve the effect that you want.
>I think that it should say that the predicate determines the meaning of any

? What does that mean? (I can only interpret it as something that is 
obviously false, so I must be misunderstanding it.)

>It should specify in the specific case of predicate rdf:type that the
>definition of rdf:type is that the object determines the meaning of the

It cannot say that, because that is either false or meaningless. 
Rdf:type simply asserts that something is in a class; it does not 
define "meaning" (either of the term denoting the object or the 
expression denoting the class) and it doesn't really "determine" 
anything, since at best it can only be said to *constrain* possible 
meanings, rather than uniquely determine a meaning.

>It should then hand off to the URI spec to say that "determines" above means
>that those publishing issuing or owning terms are the ones who definitively
>define (through specs etc) what they mean.

But that is impossible in RDF, since the full 'meaning' of a term 
depends on the total graph of which it is a part, and this may have 
been assembled from a variety of sources. So these sources all 
contribute to the 'meaning' of the term; it cannot be said to derive 
solely from any one of them.

>  Issues of
>ownership, and dereference are covered not in the RDF spec but
>directly or indirectly in the URI spec.
>>     o Whilst the RDF specs might say what a statement means, that meaning
>>  might be modified by its context.  For example, what about an RDF graph
>>  entitled "Myths about Namespaces".  Would the publisher of that graph be
>>  asserting the statements therein?
>*** The role of the RDF spec is to state what an RDF document means. ***

What the RDF spec says is that the meaning of an RDF graph is 
expressed by the RDF model theory, and what that means is, roughly, 
that the meaning of an RDF graph is expressed as a constraint on the 
world being described, that it must make the graph true. Each 
document defines a graph.

If you have something more in mind by 'state what an RDF document 
means', then please tell us what it is. If by 'meaning' you mean 
something like a single unique meaning that can be determined 
computationally, then it is impossible for any spec to provide it. 
That is not a reasonable expectation for any formal specification.

>The role of SMTP spec to say that a message delivered under certain
>circumstances is
>a message from one party to another.
>In other words, other protocols deal with the question of who is asserting
>Typically these things are complex and recursive, but the common point of
>reference is the meaning of a document.

I really think it would be more useful if you didn't take this line, 
as it doesn't lead anywhere. There is no such thing as THE meaning of 
a document, particularly of a document in a formal language. There 
are several precisely defined variations on 'meaning' that you could 
use: for example, we can say what it means to draw a valid conclusion 
from a document, or what it means for two documents to be consistent 
with each other, or what it would mean for a document to be true; but 
we cannot say what a document 'really means'.

>>     o Some on the WG do not believe that the WG is empowered to make law;
>>  that is a matter for the lawyers, governments, parliaments and the like of
>>  the many countries of the world. Different countries may make different
>They are right, RDF Core cannot determine the punishment to meted out to
>an individual who makes a false statement in  given case and
>a given jurisdiction. However, it is vital that RDFCore explain concisely
>unequivocally the algorithm for  determining the meaning of an RDF document

?? What algorithm for determining meaning? (Do you mean, algorithm 
for checking validity of inference? We can do that.)

>so that legal folks have a sound base for their own arguments, but no
>basis for wriggling out between the specs.
>Note that RDF specs are referred to by XML specs (via the namespace)
>which are referred to by the MIME registry which is referred to by the HTTP
>spec which is referred to by the TCP port registry, which is referred to
>by the TCP spec, which you effectively agree to when you get an IP
>So there is a well accepted and important chain of delegation, in which
>RDF plays a role of one link.

Until you get to RDF, this is all to do with computable operations 
over computable domains, so has well-defined notions of meaning based 
on fixed-point semantics. RDF is where it starts talking about the 
wider world outside the recursive universe of computational 
processes, and that is where 'meaning' suddenly gets far more 
difficult to pin down. The universe as a whole does not satisfy the 
second recursion theorem.

>(See my www2002 keynote)
>>     o Do you expect us to define exactly what an RDF statement means?
>>      _:b <rdf:type> <foo:Liar> .
>>      _:b <foo:email> <mailto:bwm@hplb.hpl.hp.com> .
>Yes. By delegating to the specification of the Properties and Classes
>used as predicate and (in the case of rdf:type predicate) object.
>>  What chain of evidence would be required to prove that this is  a
>>  derogatory statement about me.
>The chain would be  that I mentioned above showing that the
>definitions of foo:Liar and foo:email define the meaning of the document.

But there are no definitions in RDF. So this can only mean, at best, 
that there are some RDF assertions (in a graph somewhere) which are 
sufficient to constrain the possible interpretations to those worlds 
in which Brian is, in fact, a liar. And that in turn requires that 
the concept of 'liar' is somehow expressible in RDF, which is a 
pretty ambitious claim to make. Suppose Brian sued me and I said in 
response that the term 'foo:Liar' was not intended to express the 
derogatory English meaning of the English word "liar", and challenge 
him in response to show how any conclusion that would be harmful to 
him could be derived as an RDF-valid entailment from my RDF graph. 
Would that be a reasonable defense, in your view? I would find it 
convincing, myself.

>To then show an HTTP response from server for foo, which has
>been, though established social procedures and technical specs of DNS been
>delegated the ability to publish information by the owner of the foo.
>That response could contain information in a suitable language

What does 'suitable language' mean? Does it have to be suitable for 
use by RDF reasoning agents?


Indicated to what/who? To a human reader, or to a software agent? 
(Does the software agent only know RDF, or does it also know DAML or 

>foo:Liar was a class of people who were liars, and that foo:email was
>an emailmox which a person used, then the chain would be complete
>about the meaning of the document.
>There is a simple step to show that no one else has your mailbox.
>Now suppose that document were published by sending it to
>a public email list.  There is an indisputable body of history which
>accepts that such a message is considered a public assertion by the sender.
>So you could sue.

Yes, but you would be suing because it was a public assertion *in 
English* to *human readers*, which has got nothing at all to do with 
RDF. The same slander case would probably work if RDF wasn't involved 
anywhere, and you just had the character string 'Brian McBride est un 
fichu menteur' on the web page. (Notice the use of quotation in the 
previous sentence to mention, rather than use, a character string.)

>  You couldn't if the document were sent in an attachment
>as attachments break the chain, unless there is a something in the cover
>(e.g. "I agree with the enclosed") to connect the chain of assertion.
>It is arguable what happens if it is published
>on a website.  Normally it is clear (for example though links from someone's
>home page) which documents published are deemed to be asserted, and which
>are archive copies of other people's things, for example.

Sure, but here you are talking about human assertions, right? That 
is, assertions made in the context of human society and human 
discourse, using human language. RDF isn't a human language; it's a 
new kind of thing: a formalism for use by software agents which is 
also public in a human world. I wonder if the courts are ready for 
this; I suspect they will have to deal with a whole new set of issues 
that have never arisen before.

>  In other cases,
>there is explicit link from elsewhere -- such as a chumping in IRC which
>agrees with the doc.
>>  The current model theory WD
>>     http://www.w3.org/TR/rdf-mt/
>>  in section 1.3 states:
>>     [[Asserting an RDF graph amounts to claiming that it is true, which is
>>  another way of saying that the world it describes is, in fact, so arranged
>>  as to be an interpretation which makes it true.
>>     ]]
>>  Is this sufficient to meet your needs?
>No.  I would not want the above to be dependent on the Model Theory at all,
>but asserted in the RDF spec.

But the spec says that the model theory defines meanings. That is 
what an MT is *for*, to define meanings.

>The model theory does not as far as I know have such a spec hand-off, which
>is essential to the meaning of RDF.  It only considers things you can know
>by only taking into account the RDF spec, and so, while it gives a mapping
>of RDF into set theory

That isn't right. It doesn't map RDF into set theory or indeed into 
anything else. It gives a mathematical account of the *relationship* 
between RDF and possible ways the world could be. It uses set theory 
to describe the world in mathematical terms, because its a 
mathematical theory; but it treats RDF simply as RDF.

>, it does not as far as I could see explain what an
>RDF document means.

Without a model theory (or some kind of semantics) it doesn't mean 
anything. As far as I can see, this is the ONLY way that one could 
explain what it means.

>  (Maybe I am wrong and I missed it).
>>  Other means would be needed to
>>  establish that a statement was about the world we live in and that it was
>>  being asserted.  It seems that such claims could only be established from
>>  the context in which the statement was used.
>So RDF for those claims relies on other specs which invoke RDF.
>The RDF Core group should just define the meaning of an RDF document.
>>  The RDFCore WG has discussed other possible statements that it might
>>  make.  The following text, which might be included in the primer,  was
>>  suggested for discussion:
>>  [[
>>  Assertions made in RDF are analogous to assertions made in any other
>>  language. The author and/or publisher of these assertions is responsible
>>  for these assertions. It remains the responsibility of courts to determine
>>  legal responsibility considering the effects of context and other factors.
>>  ]]
>I think reference to the other specifications which invoke RDF is more
>useful here.
>It is *NOT* a good idea to give the slightest indication that you leave to
>the courts
>any discussion of the connections between IP, TCP, SMTP, MIME, XML and RDF

Sure, because these are all technical matters than can be determined 
by computers. But there is a final step, between RDF and the *actual* 
world that it is supposed to be talking about, that is suddenly not 
computable, and ultimately will, I suspect, have to be determined 
socially; that is, by the courts, in the final analysis.

>  > Brian McBride
>  > RDFCore co-chair
>Tim Berners-Lee

Pat Hayes

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Received on Wednesday, 29 May 2002 15:43:15 UTC

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