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Re: Subjects as Literals

From: David Booth <david@dbooth.org>
Date: Wed, 07 Jul 2010 09:23:29 -0400
To: Henry Story <henry.story@gmail.com>
Cc: Linked Data community <public-lod@w3.org>, Semantic Web <semantic-web@w3.org>
Message-ID: <1278509009.13675.7514.camel@dbooth-laptop>
On Wed, 2010-07-07 at 10:33 +0200, Henry Story wrote:
> On 7 Jul 2010, at 04:23, David Booth wrote:
> > On Tue, 2010-07-06 at 20:45 +0200, Henry Story wrote:
> > [ . . . ] 
> >> foaf:knows a rdf:Property .
> >> 
> >> Well we can dereference foaf:knows to find out what it means. This is
> >> the canonical way to find it's meaning, and is the initial procedure we
> >> should use to arbitrate between competing understandings of its meaning.
> > 
> > Right.  The document you get upon dereferencing -- the "follow your
> > nose" document -- acts as a URI declaration.[1]
> > 
> > 1. http://dbooth.org/2007/uri-decl/ 
> Yes, very interesting and useful paper. 


> I can't say if I agree with all of it yet, as I would have to read it
> more carefully.  But I think reflection in this space is very much
> needed. 

It's been a few years since I first wrote it, so I should probably
re-read it to see whether *I* still agree with all of it.  :)

> A few notes. 
> You use the word "URI" a lot in your paper, but I am not sure all URIs
> have a dereferencing mechanism. What is interesting about your paper
> is that it points to a reason for why this is really important part of
> a URI.

> It would be interesting to make the case in terms of the Fregean
> Sense/Reference distinction. I have used that to explain "How does
> Secure Authentication Work with FOAF+SSL?" in the FAQ
>   http://esw.w3.org/Foaf%2Bssl/FAQ
> On the sense reference distinction, I think people tend to forget that
> in the semantic web, every URI we use is a relation between a string
> and a thing, intermediated by the sense.
>   We could make this clear by creating the reference relation, perhaps
> log:reference
> which would relate a URI string to the thing.
>   <http://bblfish.net/#me> owl:sameAs "http://bblfish.net/#me"^^log:reference .
> this makes it clear that the <...> notation is just the shorthand for
> the literal notation to the right, which if thought of this way,
> suggests we have been using literals in subject position all the
> time ;->

Nice.  And I agree that this kind of relation is needed.  But are you
making an intentional distinction between log:reference and the existing
log:uri relation?
Before I noticed log:uri I made up a similar relation (though I hadn't
used it as a datatype), but I have since been using log:uri to express
this idea:

   <http://bblfish.net/#me> log:uri "http://bblfish.net/#me" .

>   So what is log:reference do? Well it is the relation that gives the
> reference of an object. But how does anyone come to know the procedure
> for finding the reference? (This is a very Michael Dummett like
> question). If there is no way to find the sense of a word, if there is
> no thing to learn that counts as knowing it, then there is no way of
> being right or wrong about its use. And so the word has no meaning. 
>   In everyday human life for millennia there have been certain skilled
> user of a word, masters of the vocabulary, that are final arbiters of
> the words meaning. This has to be true in the semantic web too, but we
> need more mechanical ways of finding the sense.
>   So to repeat: the log:reference has to be a relation that links the
> name to the referent via the sense. Since it is tying a string to a
> thing, it has to get going on information from the URI string. The
> only way of doing that is getting that string's log:semantics: ie
> dereferencing that string using the canonical method for dereferencing
> that URI given its scheme. A http URL is dereferenced using the HTTP
> scheme, a ftp url using the ftp scheme, https using http and TLS,
> etc.... 

Take a look at "Resource Identity and Semantic Extensions: Making Sense
of Ambiguity":
which was presented at the Semantic Technology Conference two weeks ago.
It sheds some light on issues of resource ambiguity, and it proposes a
standard way -- basically an attempt to codify common practice -- to
determine a URI's referent.
>    The document returned has to be interpreted giving us its
> log:semantics. Perhaps it would be more helpful to have the canonical
> semantics relation (and perhaps this is what named graphs are?)
>    "http://bblfish.net/#me" log:canonicalSemantics #at a time?
>                { :me a foaf:Person;
>                      foaf:name "Henry Story";
>                      foaf:homepage <http://bblfish.net/>;
>                      is cert:identity of ... } .
>   Notice now that the object of log:canonicalSemantics is a graph, which
> we can think of as the set of possible worlds in which the statements therein
> are true.
>    I think up to here I feel pretty comfortable.
>    There are a few interesting issues from there on that I need to
> think about more:
>    - if the graph to the right does not individuate one thing, is that
> just bad practice? Does it make the url "http://bblfish.net/#me"
> essentially unuseable, until that detail is cleared up.

No, that does not (necessarily) indicate bad practice.  See myths #1 and
#3 in

>    - how much of the vocabulary inside the graph needs to be
> understood too? Perhaps
>  one needs to get the meaning of each relation until one finds an
> identifying description.

Yes.  Ideally, one should obtain the transitive closure of dereferencing
each URI to its URI declaration -- the "ontological closure".  This is
described in

See also the proposed responsibilities and expectations of the URI
owner, RDF statement author and RDF consumer described in "The URI
Lifecycle in Semantic Web Architecture", from the 2009 IJCAI workshop on
Identity and Reference:

>    - Is the description in the graph to the right a way that would
> identify :me in every possible world, ie is it a description or a
> rigid designator? How does one distinguish rigid designators from
> general desciptions.

No, in general it will be ambiguous.  However, the nice thing about it
is that the ambiguity is precisely bounded.

>      I think your suggestion here is that it is a rigid designator --
> which it can only be if there is a way to tie that meaning to the
> actual world.  You do this tying to the actual world by thinking of
> the description as a speech act, or a document publication act. That
> sounds good.  
>    But perhaps we need a vocabulary then to help us distinguish such
> acts and general descriptions. 

Yes, and that is the general distinction between "core assertions" and
"auxiliary assertions".

I used to think that a speech act was more important.  But the important
thing is not the speech act itself, it is that RDF statement authors and
RDF consumers *believe* that the URI is tied to a particular meaning.
And what's needed for that is simply an agreed, standard mechanism for
establishing and determining the meaning.  This is the basic idea of
establishing the roles and responsibilities of the URI owner, RDF
statement author and RDF consumer.

> I think a few examples would probably help here. If all the graph
> contained was
>     { :me foaf:name "Henry Story" . }
>    Then that certainly would be ambiguous. Would that mean the
> <http://bblfish.net/#me> then referred to any person named "Henry
> Story" ? In any possible world? 

Yes.  And as an interesting aside, a bnode has an empty URI declaration.

>      In the foaf+ssl space perhaps it does not matter because all the
> authentifying server knows is that a certain thing at the end of the
> actual connection was able to encrypt something with a private key
> which then matched the public key. From then on that server has two
> pieces of information: it has a description + it has information about
> an actual causal connection that took place, which then identify
> uniquely an actual agent. Once that piece of knowledge is added to the
> data store, that agent will in all further interactions be able to
> increase its causal access to that agent.
>  Anyway, I think these things are tricky but solveable, and somehow we
> are on the right track. 

I agree.  I think the main thing that is needed is to further clarify
and codify the right guidelines.  

> Speech act, sense/reference, all are important parts of the puzzle. 
> Gareth Eveans btw in his book "The Varieties of Reference" has a very
> important contribution here concerning the relation between
> determinate descriptions and reference..... 
> 	Henry Story

David Booth, Ph.D.
Cleveland Clinic (contractor)

Opinions expressed herein are those of the author and do not necessarily
reflect those of Cleveland Clinic.
Received on Wednesday, 7 July 2010 13:23:58 UTC

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