Re: Comments on Section 3

   Date: Tue, 15 Apr 2003 16:29:41 +0100
   From: Dave Reynolds <der@hplb.hpl.hp.com>
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   CC: "David R. Karger" <karger@theory.lcs.mit.edu>, matsakis@MIT.EDU,
      www-rdf-dspace@w3.org
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   Kevin Smathers wrote:
   > 
   > On Mon, Apr 14, 2003 at 06:17:09PM -0400, David R. Karger wrote:
   > 
   > > I feel the same way about statements (I'm not going to try to define
   > > facts).  An "a R b" statement is unique.  If two people make the same
   > > "a R b" statement then that is exactly what happened: they asserted
   > > the SAME statement.
   > 
   > Just because the content of the statement is identical doesn't mean that
   > you can validly collapse all of the statements with that content to a
   > single instance.  The content will remain identical even if there are
   > multiple instances, but the address distinction between the statements
   > will be lost if the instances are collapsed.  Neccessarily therefor,
   > collapsed statements represent a loss of information.

   Some terminology that might help with this discussion is that of
   "statements" and "statings" (see the RDF Core WG discussions on
   reification). A "statement" is the abstract thing, of which there
   is only one for each "a R b". A "stating" is the occurrence of some
   statement in a context (e.g. in some XML file or database).

I don't think that the placement in context changes the fact that
there is but one "a R b" statement.  I do draw a clear distinction
between a statement and an _assertion_, which I think is close to your
notion of stating but which, rather than being about context, is about
some entity actually declaring that statement to be true.  One might
wish to do this by using the statement "joe asserts (a R b)", but this
puts us into an infinite regress.  The minimal fix is to allow some
kind of signature on the "joe asserts ..." statements that indicate
that joe really did assert.

   The WG decided that an RDF reification represents a stating rather
   than a statement, so there can be more than one for each "a R b"
   triple.

This seems problematic.  I had been told that one of the points of
reification was to let someone talk about a statement without stating
it; are you now saying the opposite?

   Statements don't have "addresses" so there is no address
   distinction to maintain. Reified statements do have addresses,
   URI's or bNodes.

Yes, and I think the URI of the reified statement should be an MD5 of
the statement.  This means I think that there is only one name to
represent the reification of a given statement.  But I don't see this
as a problem.  It is perfectly reasonable for two different
repositories to contain assertions about a given statement, assertions
that may contradict one another.

   Thus I would suggest that both people are asserting the truth of
   the same "statement" but are doing so via different "statings". If
   you wish to represent the stating explicitly within the RDF data
   model then use reification. As defined in the RDF Model theory you
   can't collapse multiple reifications (statings), they are different
   resources, but you *can* collapse multiple statements.

Indeed, the statements "Joe asserts statement" and "Dave asserts
statement" are distinct statements (but each can now be named by an
MD5 URI)

   > Your argument that the users intent all along should have been to
   > assert the same instance as had been asserted previously is presuming
   > to know the intent of the user.   If the user had that intent, then
   > there is no reason for them not to use the preexisting statement
   > directly.

"assert the same instance" is a circular objection.  It implies there
is more than one instance of a statement.  I see no point to having
such.

   Not sure that is ever a good idea. If Jim asserts "a R b" using a
   stating with URI "S1", then Jill asserts "a R b" I'd prefer to note
   that as another stating with a different URI (address) "S2" - after
   all they have different provenance.  I'd rather Jill did not try to
   pretend that she made stating "S1" even though she did assert the
   truth of the same abstract statement "a R b".

What is important about the two statings is that they are different
statings (one is "Jim says ..." and the other is "Jill says ..."), not
that they have different names.  The fact that they have different
names is a consequence of their being distinct.

Received on Tuesday, 15 April 2003 11:58:37 UTC