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RE: Revised draft of CBD

From: <Patrick.Stickler@nokia.com>
Date: Sun, 10 Oct 2004 14:07:50 +0300
Message-ID: <1E4A0AC134884349A21955574A90A7A50ADD24@trebe051.ntc.nokia.com>
To: <otto@math.fu-berlin.de>
Cc: <eric@w3.org>, <pfps@research.bell-labs.com>, <www-rdf-interest@w3.org>



> -----Original Message-----
> From: ext Karsten Otto [mailto:otto@math.fu-berlin.de]
> Sent: 07 October, 2004 15:22
> To: Stickler Patrick (Nokia-TP-MSW/Tampere)
> Cc: eric@w3.org; pfps@research.bell-labs.com; www-rdf-interest@w3.org
> Subject: Re: Revised draft of CBD
> 
> 
> Hello,
> 
> 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".

Agreed.

A significant, but complementary, distinction that I see between CBDs
and SCBDs is the difference in focus between facilitating a intersection
of ontological commitment between automated agents operating on behalf
of human users (CBD) versus facilitating an intersection of
ontological usage between users employing automated agents (SCBD).

(comments below about what you call a CBUD)

There are two different sorts of questions that can be asked given
a particular URI:

1. What does this URI mean? I.e. what are the inherent characteristics 
   of the resource denoted by this URI.

2. How is this URI used? I.e. what are the relationships of the resource
   denoted by this URI with other resources.

Granted, there will usually be an intersection in the answers to both
of these questions, but the questions, and their use cases, are 
nonetheless distinct, as are the form of the answers.

The answer to the first question should be, IMO a CBD.
The answer to the second question could very well be an SCBD.

I think these two use cases are complementary. In fact, one can
see the first use case as a specialization, or inherent component, 
of the second, which is reflected by the fact that a CBD is a subset 
of a SCBD.

Many (most?) agents (especially mobile/embedded agents) will be very 
selective about the information desired/needed per a given URI, and 
will be concerned primarily about shared ontological commitment with 
the other agents it communicates with, and ask for CBDs. 

Other agents may be looking at the broader scope of usage, and thus 
will ask somewhat broader questions about the URIs they encounter, 
e.g. they will ask for SCBDs.

Having CBDs as a default, but having both CBDs and SCBDs 
defined in a standardized way so that broad support for both can
be encouraged and either can be easily requested, would be IMO
a very good thing.


> 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.)

If I understand this correctly, a CBUD would be a subset of a SCBD,
right?

I don't suppose you could provide an example, per the node
http://example.com/aReallyGreatBook in the source
graph provided in the latest CBD document:

http://swdev.nokia.com/uriqa/CBD.html#sourcegraph

???


> 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.


Fair enough. Though note that this would make a CBUD incompatible
with the URIQA interface (the same for IFCBDs) and thus, while
offering clear utility, impose greater implementational requirements
and communication overhead than either CBDs or SCBDs, so if a CBUD
is a subset of a SCBD, would a SCBD suffice?

And if a CBUD is not a subset of a SCBD, per the present definition
of an SCBD, it may be reasonable to modify the definition of an SCBD
accordingly to address your use case while still allowing effective
use of the minimal URIQA interface.

Cheers,

Patrick

 
> Regards,
> 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 Sunday, 10 October 2004 11:08:20 GMT

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