- From: Stefan Decker <stefan@db.stanford.edu>
- Date: Sat, 13 May 2000 09:24:45 -0700
- To: Sean Luke <seanl@cs.umd.edu>
- Cc: www-rdf-interest@w3.org
Hi Sean, > > > Also, as I understand it way namespaces are used in RDF is > > > only to uniquely identify what object you're talking about, not which > > > sets of definitions you subscribe to. Thus, if I state that I am > > > Web_Developer, then do I also imply that I am a Silly_Person? > > > > If you say P and P->Q, then you imply Q, yes. But > > if you say P and somebody else says P->Q, then a third > > party may or may not decide to trust you both enough > > to conclude Q. > >What if a third party Foo says P->Q, you rely on this to make all sorts of >statements about P under the assumption that your clients will use Foo's >claim to understand that you're really talking about Q, and then Foo drops >off the face of the earth? Say, because the ILOVEYOU virus brings down >their system for a week. They're still very trustworthy: everything they >say is true. But right now they're not saying anything, and your clients >don't find their stuff and so interpret your semantics in a different way >than you did when you posted your data originally. Or Foo updated its >claims and dropped a few statements that you relied on, not knowing that >you were doing so. You're left hanging in the wind. But i want to define links between knowledge pieces and point to different servers on the web. I have to deal with glitches then, but i also have to deal with the same glitches now (eg. when i encounter a broken link in a HTML page). >It seems to me that trust isn't a great model for this kind of stuff in a >distributed, uncontrolled environment. I think that dealing with the >weirdness caused by a lack of control inherent in a distributed system is >one of the features that RDF needs to work more on. Because RDF lets >"anyone say anything about anything", with no notion of authority at all, >then people are free to redefine the semantics of a language in a very >fine-grained, highly distributed fashion. Combine this with a cooperative >reliance on who said what about what in order to understand the proper >semantics of some claim X, and you're gonna see a lot of semantic >misinterpretation as little parts of the distributed RDF web come up and >down. > >SHOE's model counters this in two ways, which Jeff is getting at I think. >First, it separates schema from data, which at least attempts to provide >*some* semblence of authority, or at least a well-defined semantic >language so we're very clear on what I intend to be inferred when I say >thing Foo. But is actually also possible for RDF. An RDF-Schema (or Sergeys UML-RDFSchema) can define any language for RDF. One is free to adopt a formal semantics for the language if this is useful - this is actually the way currently OIL goes (see http://www.ontoknowlege.org/OIL ). So you have the same separation of schema and data - with the freedom to define any Knowledge Representation Language on top of RDF - and i don't just count logic based formalisms as Knowledge Representation Languages. What about Petri Nets or finite state machines (see again Sergeys UML model) (which are used to represent dynamic knowledge in a declarative way)? How would a Petri Net (and instances of Petri Nets) be defined in SHOE? >RDF would work great in a "sandbox environment" typical of most KR >systems, where the system has the entire body of knowledge (so to speak) (RDF is not a Knowledge Representation system at all. RDF just provides a lightweight object model to define other languages on top of RDF - not necessarily typical KR languages.) >stored internally and so can interpret statements in its system under the >semantics of the full universe of facts at its disposal. But I think that >RDF does not take into consideration the uncomfortable fact that the web >is not a sandbox. People say anything they want, even trusted ones. And >they can stop saying these things at any time, and for any reason. >Relying on the availability, correctness, and completeness of others' >statements in order to put your own into context is pretty dangerous. Isn't it equally as dangerous to a link to another HTML-page from your own page, since you can't guarantee that the other HTML-page will be available an hour late? I agree: one can't rely on concepts like correctness and completeness in the conventional use anymore (as eg. known from Reasoning in First-Order Logic). So we need to find other concepts. Best, Stefan
Received on Saturday, 13 May 2000 12:17:57 UTC