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Re: problems with concise bounded descriptions

From: Benja Fallenstein <b.fallenstein@gmx.de>
Date: Fri, 01 Oct 2004 16:42:47 +0200
Message-ID: <415D6CE7.3030602@gmx.de>
To: Patrick.Stickler@nokia.com
CC: pfps@research.bell-labs.com, www-rdf-interest@w3.org


Hi Patrick, hi Peter--

wow, it certainly looks like there are some communication problems here! 
;-) I thought maybe it would help at this point if an outsider steps in 
and tries to explain where it seems that you don't understand each 
other. Hope this helps -- sorry if it's just more noise...

I believe that there are at least two general problems that Peter has 
with the specification. First, the much discussed paragraph:

     A concise bounded description of a resource is a body of knowledge
     about that resource which does not include any explicit knowledge
     about any other resource which can be obtained separately from the
     same source.

Aside from the details you've discussed, the more fundamental issue is 
that Peter sees this as a *definition* of CBD: i.e., everything that 
fits this description is a CBD.

Then, he argues, "always return an empty graph, no matter what knowledge 
you have" is a procedure that generates a CBD, according to the above 
definition.

Seeing the context, I don't actually believe that Patrick meant the 
above paragraph to be a *definition* of CBD, but just as a description 
of some traits of CBDs. After all, the document only purports to define 
"a concise bounded description of a resource *in terms of an RDF graph*" 
(emphasis mine), and there is an entire section called "Definition."

However, *if* the paragraph above was meant as a general definition 
(independent of the notion of an RDF graph) of what a CBD is, then Peter 
is right: by that definition, a correct procedure for obtaining a CBD 
would be to just always use the empty graph, no matter what knowledge 
you have about a resource; then the notion of "CBD" wouldn't be very 
useful. *If* the paragraph is intended to define CBD, it would be more 
useful to refine the definition to make sure that if useful information 
is known about a resource, it is part of the resource's CBD.

The second problem that Peter sees is with the actual definition of CBD 
(you know, the one in the section called "Definition"), which says:

     Given a node in an RDF graph which occurs as the subject of one or
     more statements in that graph, the concise bounded description of
     the resource denoted by that node is the subgraph of statements
     comprised as follows:

     1. Include all statements where the subject of the statement denotes
        the resource in question; and
     2. Recursively, for all statements included in the description thus
        far, for all anonymous node objects, include the inverse
        functional bounded description of the anonymous resource as
        follows: (...)

Now, Peter's point is that the server generally cannot know which nodes 
in the graph "denote the resource in question." However, it is not 
possible to perform the process as defined above without knowing which 
nodes denote this resource.

The obvious fix is to just say "Include all statements where the subject 
of the statement is the node in question."

I'm not sure that this is what Patrick wanted, because he could easily 
have written that. Perhaps what he meant was "Include all statements 
where the subject of the statement is *known* to you to denote the 
resource in question." This would mean that in the following graph:

     ex:a    ex:b    ex:c
     ex:a owl:sameAs ex:d

the CBD of ex:d would include the statement

     ex:a    ex:b    ex:c

since its subject denotes the resource in question (namely, the resource 
denoted by ex:d).

However, this complicates the process and doesn't really add much: It 
assumes that the server has inference capabilities, and if so, it can 
certainly inference that

     ex:d    ex:b    ex:c

which would then be part of the CBD of ex:d according to the definition 
"Include all statements where the subject of the statement is the *node* 
in question."

I therefore suggest that it would be sensible to change "resource" to 
"node" everywhere in the definition (making the appropriate adjustments 
to the context). I believe this would address Peter's concerns.

I hope that maybe this mail can help a bit. It's a pity to see you guys 
slipping into flame mode ("Whatever you're smoking, can I please have 
some?" ;-)) because (it seems from outside) you're not getting your 
valid points across to each other.

Cheers,
- Benja
Received on Friday, 1 October 2004 14:43:32 GMT

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