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Re: Revised draft of CBD

From: Karsten Otto <otto@math.fu-berlin.de>
Date: Thu, 7 Oct 2004 14:22:20 +0200 (CEST)
To: Patrick.Stickler@nokia.com
cc: eric@w3.org, pfps@research.bell-labs.com, www-rdf-interest@w3.org
Message-ID: <Pine.LNX.4.61.0410071331090.3519@hobbes.mi.fu-berlin.de>


Congratulations on the revised CBD document[1]. I find it very helpful to
put CBDs in the right light, in particular the sections on application
issues. I'm also glad to have to original CBD back :-)

Reading through the section on alternative forms reminded me of a
point raised by Eric Prud'hommeaux [2] about "arcs-in" knowledge.
The Symmetric CBD is a partial solution to this issue, but not in
cases where no symmetric properies exist. As a practical example,
during graph inspection I sometimes find myself in need to ask the
question "tell me *who uses* this resource".

While this departs from the original CBD question of "tell me about this 
resource", I believe it to be a common enough case to deserve its own 
"optimal alternative form". This Concise Bounded Usage Description (CBUD)
can easily be dervied from the original CBD definition by exchanging 
"subject" and "object", plus a minor modification regarding reifications:

1. Include in the subgraph all statements where the *object* of the
    statement is the particular node in question;
2. Recursively, for all statements identified in the subgraph thus far
    having a blank node *subject*, include in the subgraph all statements
    where the *object* of the statement is the blank node in question
    and which are not already included in the subgraph.
3. Recursively, for all statements included in the subgraph thus far, for
    all reifications of each statement, include the *four RDF reification
    statements* and the concise bounded *usage* description of the
    rdf:Statement node of each reification.

(Note that one could also construct symmetric and inverse functional 
variants in a similar way when needed.)

I find this definition useful for a number of reasons:
Rule 2 helps to determine usage relations across one or more anonymous 
nodes, commonly found in rdf:value constructs. Without this, finding such
indirect usage relationships would require a number of extra queries.
Rule 3 extends the information to usage of reifications involving the
queried resource. Again, a number of extra queries would be necessary to
determine that this usage is actually part of a reification, and to find
the users of it in turn.

I would be interested in your opinion on this issue.

Karsten Otto

[1] http://swdev.nokia.com/uriqa/CBD.html
[2] http://lists.w3.org/Archives/Public/www-rdf-interest/2004Oct/0001.html
Received on Thursday, 7 October 2004 12:24:55 UTC

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