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Re: Distributed querying on the semantic web

From: Phil Dawes <pdawes@users.sf.net>
Date: Mon, 19 Apr 2004 22:03:05 +0100
Message-ID: <16516.16010.922.461826@gargle.gargle.HOWL>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
Cc: www-rdf-interest@w3.org

Hi Peter,

From what I can gather, your concerns and objections are based around
issues of trust and authority - neither of which I attempted to
address in the original mail. I am purely attempting to address
the problem of information discovery in the early stages of the SW.

Answers inline:

Peter F. Patel-Schneider writes:
 > From: "Phil Dawes" <pdawes@users.sourceforge.net>
 > Subject: Distributed querying on the semantic web
 > Date: Mon, 19 Apr 2004 12:48:02 +0100
 > > Hi All,
 > > 
 > > I like Patrick Stickler's assertion that in order to participate in
 > > the 'semantic web', http URIs should be dereferencable to some
 > > information about the URI. 
 > I believe that you meant information about the referent (denotation, meaning,
 > ...) of the URI.  If all that is available is information about the URI,
 > then this is not very interesting, as I really don't need to know much
 > about a URI.

Yes - sorry if that wasn't clear.

 > However, I do hope that you did not mean necessary information about the
 > referent (denotation, meaning, ...) of the URI.  I vigorously oppose any
 > attempt to require that part of the meaning of a URI that my applications
 > are supposed to abide by be the meaning that can be found in a document
 > found by dereferencing the URI.  To pick my favourite example, I do not
 > want my applications to be required to abide by the information available
 > at http://www.whitehouse.gov just because I use the URI
 > http://www.whitehouse.gov/#GeorgeWBush, *even* if this information is only
 > something like
 > 	http://www.whitehouse.gov/#GeorgeWBush rdf:type foaf:person .

If your application is going to use information gleaned dynamically
from the web, then you're going to have to deal with this somehow.

 > > I am considering how an infrastructure
 > > could be built where this could be exploited for distributed queries.
 > > 
 > > The main problem with Patrick's concise-bounded-description idea from
 > > this respect is how to find references to a term. 
 > > 
 > > For example:
 > > 
 > > (p:PhilDawes, foaf:knows, ?person) 
 > > 
 > > ..is easy to resolve - just dereference p:PhilDawes and you probably
 > > have the information you need. (I'm using dereference to mean 'look up
 > > a description').
 > Well, I'm reluctant to ascribe any status to the information thus found
 > that requires its use, and I certainly do not agree that it has to be the
 > information you need.

I'm not sure how you got the idea that it *has* to be the information
you need - apologies if I gave that impression. 
I am merely attempting to envisage a simple facility for getting
*some* information about a URI when you have none. 
At present this is impossible without using some previously-known
centralised service.

 > > However
 > > 
 > > (?person, foaf:knows, p:PhilDawes)
 > > 
 > > .is much more tricky, since these assertions are likely to be made by
 > > users external to the domain owner of p:PhilDawes.
 > Hmm.  I'm not sure of this.  For symmetric properties, it may be somewhat
 > more likely for a document to put ``local'' URI references in the subject
 > position, but what about properties that are conventionally written on way
 > around.  For example, I am more likely to write on one of my web pages
 > 	sps:Sandy ex:loves pfps:Peter .
 > than I am to write
 > 	pfps:Peter ex:isLovedBy sps:Sandy .

True. - That is a problem with 'consise bounded descriptions' as
described by the URIQA[1] proposal - this statement wouldn't appear in
the description for pfps:Peter.

 > > Here's a straw-man solution:
 > > 
 > > - In addition to its bounded description, dereferencing p:PhilDawes
 > > also provides all the references it knows about.
 > >
 > > - When people author statements refering to p:PhilDawes, they POST
 > > their triples to the description of p:PhilDawes. (Or maybe a third
 > > party does).
 > > 
 > > - The representation of p:PhilDawes polls the reference URIs it knows
 > > about periodically to keep its data up to date. (facilitating the
 > > removal of triples as well as addition)
 > Independently of the authoritative status of the accessed web page I view
 > this as extraordinarily dangerous.  There is no way that I would ever
 > subscribe to a scheme that requires any server that I have control over to
 > make responses that include
 > 	n666:antichrist owl:sameAs pfps:Peter .
 > just because some other organization has this triple in some RDF document.
 > I don't see how any responsible organization would ever subscribe to this
 > scheme, even if they could somehow tag these ``contributed'' triples as
 > having come from some other document.

That's fine. You own the domain (or at least the namespace) and so
have complete control over which triples you return in response to a
query. If people don't like what you return, they'll probably use a
different term.

I suspect that for trust to work on any implementation of an
open-world semantic web (centralised or decentralised), the authority
of a statement will have to be decoupled from the location it was
discovered. If that is the case, then it won't matter if you serve the
statement or it comes from somewhere else.

 > [...]
 > > I am keen to hear any ideas that others may have on the subject since
 > > in addition to helping bootstrap the semantic web, this is a facility
 > > that would be very beneficial in my work intranet environment.
 > I view this as a non-starter, even in a work intranet environment.  Just as
 > for the Semantic Web as a whole, there is no expectation that such local
 > environments will have a common view of the world.

Actually this already works to a certain extent (and adds value) in my
work intranet environment. We have a facility (in use) that returns
RDF contact information for an employee by dereferencing the HTTP URI
denoting that employee (via a 301-see-other). N.B. This only works
because the applications using the facility trust it.

Without such a facility on the semantic web, I struggle to see how it
will be bootstrapped to deal with open queries. At present, there is
no real 'web' of information to search.



[1] http://sw.nokia.com/uriqa/URIQA.html
Received on Monday, 19 April 2004 18:04:24 UTC

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