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RE: Concise Bounded Descriptions - updated, expanded, stand-alone definition

From: <Patrick.Stickler@nokia.com>
Date: Fri, 20 Aug 2004 13:52:28 +0300
Message-ID: <A03E60B17132A84F9B4BB5EEDE57957B02A2E9EB@trebe006.europe.nokia.com>
To: <otto@math.fu-berlin.de>
Cc: <www-rdf-interest@w3.org>



> -----Original Message-----
> From: www-rdf-interest-request@w3.org
> [mailto:www-rdf-interest-request@w3.org]On Behalf Of ext Karsten Otto
> Sent: 20 August, 2004 13:08
> To: Stickler Patrick (Nokia-TP-MSW/Tampere)
> Cc: www-rdf-interest@w3.org
> Subject: Re: Concise Bounded Descriptions - updated, expanded,
> stand-alone definition
> 
> 
> 
> On Thu, 19 Aug 2004 Patrick.Stickler@nokia.com wrote:
> 
> > A draft of an updated, expanded, stand-alone definition for Concise
> > Bounded Descriptions is now available
> >
> >   http://swdev.nokia.com/uriqa/CBD.html
> >
> [snip]
> 
> Great to have this on its own page as a point of reference!
> However, I have a problem with the new concept of the inverse 
> functional
> bounded description: It requires that both the sending and receiving
> agents are schema/ontology-aware, and also that they share the same
> schema/onology-knowledge, in order to correctly create and interpret a
> CBD.
> 
> For once, the sender needs to know that a given predicate is an
> owl:InverseFunctionalProperty, so it can pick the "if"-branch of the
> IFBD definition for an anonymous resource. However, this knowledge
> may not always be available, e.g. in case of a simple semantic web
> crawler. AFAIK the issue of finding all schemata/ontologies 
> for a given
> RDF graph is not solved in general yet - or is it?

If the sending agent is not aware that a given property is 
an owl:InverseFunctionalProperty, then it proceeds as if it
is not.

Then again, if the agent has no knowledge about the property,
it (ideally) would be able to submit a URIQA request to the
metadata authority and obtain the information it needs.

However, the definition/generation of CBDs still works just
fine if such information is not available -- in fact, it is
then the same as the original definition of CBDs.

> Furthermore, the receiver also needs to know that a given predicate
> is an IFP. This is a more serious issue, as it needs this to determine
> whether the "if"- or the "else"-branch of the IFBD definition 
> was picked
> by the sender. In the "else" case, it already has all known 
> statements,
> but in the "if" case it might need to issue another query (by IFP).
>
> Consequently, if the IFP is unknown to the receiver, it might falsely
> conclude that it already got all information the sender had on the
> resource.

Well, I think it is fair to presume that if the recieving agent
is going to do anything particularly useful with (i.e. make decisions
based on) the recieved knowledge, that it will have to be aware
of the vocabularies/ontologies in which that knowledge is expressed.

Also, and again, I personally do not see CBDs as a complete
solution to knowledge interchange between semantic web agents.
Something equivalent or comparable to URIQA must also exist so
that agents can further obtain the knowledge they need.

> I see two possible solutions to this problem: The CBD could contain
> the relevant "ppp rdf:type owl:InverseFunctionalProperty" statements,
> or indicate all relevant ontologies by way of owl:includes.
> However, neither solution is viable for RDF-only cases, such as
> querying the aforementioned simple spider agent.

Or, if the recieving agent has no knowledge about those properties,
it can either submit a URIQA MGET request, or ask the same source
of that knowledge for additional knowledge about those properties.
I.e., ask the sending agent what it knows about those properties
(by sending the CBD of each, etc.)

I see the definition of CBDs as a componenent of a general
bootstrapping mechanism for the semantic web, not as an all
encompassing solution to knowledge interchange.

> By the way this seems to be a more general case of the "crossing layer
> boundaries"-problem previously discussed (but not solved) in another
> mailing list thread [1].

Well, given the examples you present in that referenced document,
I would say that those "missing triples" are provided for by the
closure rules defined in the RDF model theory. Triples that can be
inferred are not the same as triples which are simply not included
in a graph, but must be obtained separately.

The whole point of CBDs is that they are *not* exhaustive -- but only
provide that information which cannot be obtained by separate queries
to the same source. The total body of knowledge which a given agent
requires to do some task will likely require the syndication of many
CBDs about many resources. CBDs are simply a useful, optimal unit
of interchange.

Cheers,

Patrick


> Regards,
> Karsten Otto
> 
> [1] 
http://lists.w3.org/Archives/Public/www-rdf-interest/2003Sep/0082.html
Received on Friday, 20 August 2004 10:53:23 UTC

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