- From: Patrick Stickler <patrick.stickler@nokia.com>
- Date: Fri, 12 Mar 2004 15:10:56 +0200
- To: "ext Chris Bizer" <chris@bizer.de>
- Cc: "ext Pat Hayes" <phayes@ihmc.us>, <www-archive@w3.org>, <jjc@hplb.hpl.hp.com>
On Mar 12, 2004, at 11:56, ext Chris Bizer wrote: > > I have serve problems with the idea that an agent owns a graph. Nobody > owns > the english sentence "Water is blue.", thus I think it is also > impossible to > own a graph expressing this sentence. > > I think we are mixing the agent/assertion/content- and the > representation/document document layer here again. > > I would see it this way: > > 1. Graphs exist in an abstract way somewhere, similar to english > sentences > abstractly existing somewhere even if nobody expresses them. I was thinking more along the lines that graphs are akin to speech acts (though I see where you might prefer to attribute speech acts to documents of some sort rather to the graph itself). This feels a bit like the Superman vs. Clark Kent quandry. We may know that Superman and Clark Kent are the same being, but we may still wish to make a distinction between the two "roles" or "personas" when making statements. Likewise, we may know that two graphs contain the exact same statements, but we may wish to make a distinction in terms of the source/authority/assertiveness/etc. of the graph. > 2. Agents can assert/deny/quote graphs, which takes place on the > agent/assertion/content-layer. Similar to me agreeing with or denying > the > sentence the "Water is blue." Thus an assertion is the relation > between an > agent and an abstract graph. Fine. But if the assertion is independent from the graph being asserted, then either we must use some extra-RDF machinery or we end up chasing potentially endless sequences of graphs, since while graph B may say that graph A is asserted, how do we know that graph B is asserted, and hence that graph B actually asserts graph A, etc. I think there is an important distinction between "asserted/affirmed by a particular agent" and simply "presumed to be asserted". Most (all?) of the "graph B asserts graph A" examples seem to have chains of the first kind which ultimately terminate in an assertion of the second kind. This bothers me alot. Since I think that reliable trust policies would need to be based solely on the first, explicit kind of assertion where the authority is always known, I just don't see how you can *ever* terminate that chain of asserting graphs (unless extra-RDF machinery is brought into play). Hence my distinction between authoritative versus third-party qualification, and the introduction of the 'bootstraping interpretation/test' which provides grounding/termination for the model. > 3. An agent can publish his assertion on the document layer. This "web > act > of publication" might have a "owner" but doesn't have to. I'm thinking > of a > graph been published as a document, then crawled and moved into a > knowledgebase by somebody else, who makes the graph accessible > afterwards > though a web query interface. This is precisely the kind of application I am also thinking about (mostly). > I think this process definitifly requires all > asserting- and provenance information been on the > agent/assertion/content-layer and not linked in any way to the document > layer. Agreed. But if it is to be done in RDF, then you have to have a means to terminate the chains of asserting graphs. And I don't see the inter-graph vocabulary interpretation providing that. > > Taking the idee that a graph is disjunct from its assertion, just as > english > sentences are disjunct from speech acts, we would get a Named Graph > representation like this: > > G1 (ex:Water ex:colour ex:blue) > > G2 (G1 trix:assertedBy ex:Chris) > > G3 (G1 trix:denyedBy ex:Patrick. > > G1 trix:assertedBy ex:Pat) ) > And how do we know who asserts G3 and whether we can trust them? I.e., you still haven't terminated your trust model and that loose end makes it useless, since trust of the assertions in G3, G2, and G1 depend on trusting whoever asserted G3. But who is it? > > The graph G1 is independent from the agent. Asserting a graph is a > relation > between the agent and the graph. > It can be done everywhere. The graphs can be moved around, stored in > different documents or repositories and whatever. Having an intra-graph interpretation constraint still allows graphs to be moved around and for different third party agents to also assert the same graph as some other agent. The key distinction is that we are able to ultimately ground the trust of our graphs in particular authorities, one for each graph. This approach also allows for non-explicitly asserted graphs, but ensures that we have the mechanism by which to terminate our chains of assertion relations between graphs and agents. E.g. G1 (ex:Water ex:colour ex:blue) G2 (G1 trix:assertedBy ex:Chris.) G3 (G1 trix:assertedBy ex:Patrick. G2 trix:assertedBy ex:Pat. G3 trix:assertedBy ex:Chris.) Now, given the ability to differentiate between authoritative assertions and third party assertions, we have a set of three graphs where we can terminate our trust determinations in some authority/agent, and can then reason backwards whether each of the graphs is to be trusted or relevant. So, starting with G3, we decide if we trust ex:Chris. If so, then we trust the statements in G3 about G1 and G2. We then decide for G2 if we trust ex:Pat, who has asserted G2 in G3, according to ex:Chris whom we trust. If so, then we trust the statement in G2 about G1. We then decide for G1 whether we trust ex:Patrick. Let's say we don't. But we do trust ex:Chris, who also asserts G1, so we can then decide that we can also trust G1. Thus, our decisions about trust are fully grounded. In the case of G3, trust is grounded in terms of the authoritative assertions, but in the case of G1 and G2 in terms of third party assertions. In the example you provided above, we were left with no place to start our deliberations, since we had no clue about who asserted G3 and whether we trusted that authority. It's not essential that every graph have an authoritative assertion, but at some point, the chains of assertions/trust have to terminate somewhere, so allowing for a special interpretation of the assertion vocabulary in terms of a particular graph as authoritative rather than third party allows for that termination. Eh? Patrick -- Patrick Stickler Nokia, Finland patrick.stickler@nokia.com
Received on Friday, 12 March 2004 08:11:26 UTC