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RE: Named graphs etc

From: Jeremy Carroll <jjc@hplb.hpl.hp.com>
Date: Tue, 16 Mar 2004 11:30:28 +0100
To: "Patrick Stickler" <patrick.stickler@nokia.com>, "ext Pat Hayes" <phayes@ihmc.us>
Cc: "ext Chris Bizer" <chris@bizer.de>, <www-archive@w3.org>, "ext Jeremy Carroll" <jjc@hplb.hpl.hp.com>

> All we have to say is that, given certain bits of information:
> 1. The URI denoting a graph
> 2. The URI denoting an authority
> 3. The signature associated with a graph.
> we have what we need to authenticate that graph per that authority, and
> check if they said what the graph expresses (regardless of whether they
> assert it).
> If the PKI machinery cannot conclude, given the above information,
> that the graph is authentic per that authority (for whatever reason,
> maybe a server was down or a signature expired, etc.) then that is too
> bad for the particular agent trying to verify a graph, but doesn't
> invalidate the basic model.
> All that matters is that we have the identity of a graph, the identity
> of an authority, and some signature to test their valid relationship.

If I have understood Pat, the MT could embed such a relationship ...


eg:g rdfg:hasSignature "...."

can either have operational semantics, RDF processors may go off and check
this, somewhat like owl:imports, or it may have formal semantics i.e. it is
true iff the bytes are a signature of the graph according to some other
document. I think it would be good to do the latter - a point which I had
been missing.

> Thus, insofar as the RDF/OWL MTs are concerned, some graph where
>     ?graph ( ?graph rdfg:assertedBy ?authority .
>              ?graph rdfg:signature  ?signature . )
> will not be automagically asserted or authenticated.

A nice thing about signatures is that the second triple cannot be
automagically generated (well not correctly), because the literal cannot be
spoofed. Thus embedding it in the formal semantics would allow me to do

  my:sig rdfs:subPropertyOf rdfg:signature

and then use my:sig instead of rdfg:signature, and everything would be
kosher and this would be robust against forged signatures (thanks to the
crypto technology).

> I think we agree here, but are having a disconnect of focus.

That's my impression too.

> So, on the one hand, we have certain claims being expressed in
> the various graphs. Some of those claims/statements provide some
> information by which the authenticity of those claims can be
> tested. Since we are interpreting those claims as valid/asserted
> claims in order to actually test those claims, it is a form
> of "bootstrapping".
> Ultimately, if the tests fail, then we reject those claims as
> invalid or untrustworthy -- essentially as not being claims at
> all, just noise.
> Yes?

That's what I understand.

> > Indeed. But we can extend the MT to give you a real place to
> > terminate. I thought that was what you wanted me in on the project to
> > do :-)
> Naahhh. We were just bored and wanted some excitement... ;-)

I don't think I was particularly aiming at one thing or another .. the TriX
paper was weak because it presented a syntax with no semantics, and it
certainly is good to have Pat on board to help with that step - I am still
not committed to any particular solution there though.

> Really, though, what we do want is *some* MT (either distinct from or
> an extension
> to the RDF MT) which provides for the special intra-graph
> interpretations needed
> to bootstrap the assertion and authentication per statements in the
> graph
> itself.

We need some thought at the semantic/MT level and some thought at the
operational level - I am not trying to prejudge what the answer is. I think
we can get overly concerned about the termination and grounding problems.

> > Well it was that layer of preprocessing stuff that seemed problematic,
> > for the reasons I suggested. Suppose to take a very simple example,
> > you have OWL statements that a class C has cardinality one and that
> > ex:thisURI and ex:thatURI are both in it and that ex:thisURI is the
> > name of a graph, and that ex:thatURI is asserted. It follows that the
> > graph is asserted, but you won't know that by inspecting the URIs
> > unless you are very OWL-savvy. Now suppose that the graph doesnt have
> > the cardinality info in it but you discover it a month later. Now make
> > the reasoning arbitrarily more complicated.
> Right. OK.
> So different agents will be able to make different determinations about
> certain graphs depending on their ability/inability to do OWL reasoning.
> But is that really breaking anything (as opposed to simply making things
> more complicated for certain agents -- which OWL does anyway ;-)

It seems to me that if we adequately articulate the bootstrapping problem
then someone who choose to publish their statements of assertion and
statements of signatures in a way that is difficult to understand will
narrow their audience. But that happens all the time - e.g. academics will
throw insults at one another in footnotes that require a load of processing
to understand - and part of that is to narrow the audience. It might even be
useful - e.g. if I want to publish my e-mail address I can put an
arbitrarily complicated OWL derivation in order to get it, this might act as
a block on spammers (of course, they already know my e-mail address).
Anyone the point is that the vocabulary does not intrinsically need to be
used in a special way to enable bootstrapping, but merely the more
straightforward usage will be understood more clearly.

> >>
> >>
> >> Defining the interpretation/testing of that special information,
> >> expressed as statements in the graph, need not intersect nor impact
> >> the RDF or OWL MTs.
> >
> > The issue is how to STOP it being involved with those MTs. I don't see
> > how that would be possible.
> Well, my original idea was that agents would be able to consider
> graphs in terms of a specialized, narrower MT than RDF/OWL which
> was just sufficient to allow them to make determinations about
> assertion and authenticity per the special vocabulary.
> I.e. the special MT wouldn't presume the full RDF/OWL MTs.

I think we can work on an orthogonal extension, which can work with RDFS or
OWL - probably not worth the effort to consider RDF (without S).

> Sort of like having a zoom lens on a camera. To test
> assertion/authenticity,
> you zoom in to apply a narrow specialized MT, and then for the rest of
> your
> processing (if satisfied with the tests of assertion/authenticity)
> you zoom out to apply the wider RDF/OWL MTs.
> The statements you zoomed in on for the narrow shot are still there
> in the wider shot, but some "special" detail may simply not be visible
> from the wider view.
> Just a thought...

I see that as a publisher's choice.


Received on Tuesday, 16 March 2004 05:31:07 UTC

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