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Re: ldp-ISSUE-75 (monotonicity): rdf:membershipProperty makes LDP PATCHing non-monotonic [Linked Data Platform core]

From: Henry Story <henry.story@bblfish.net>
Date: Mon, 3 Jun 2013 07:11:28 +0200
Cc: Linked Data Platform Working Group <public-ldp-wg@w3.org>
Message-Id: <C08206F8-6D17-4A61-A08D-52FF8E376D6B@bblfish.net>
To: John Arwe <johnarwe@us.ibm.com>

On 3 Jun 2013, at 06:35, John Arwe <johnarwe@us.ibm.com> wrote:
> 
> > > The ONLY place where you can have the default 
> > > reasoning is in the LDPC itself! 
> > 
> > Most reliable place (pesky trust issues!) probably.  Only place?  Hardly. 
> > No really.  You proved it yourself in your mail here: 
> > http://lists.w3.org/Archives/Public/public-ldp-wg/2013May/0353.html 
> ... 
> > itself. But the spec tells us that if you have the graph that came 
> > from <ldpr> that says 
> 
> I am not aware of the spec relying on any particular URL as the source of the LDPR/C triples (or any others, for that matter).  Please point out where the spec says that assertions are sensitive to source/origin in the way you describe. 

I pointed to this in a earlier mail on this thread. The spec says:

5.2.4 An LDPC must contain one triple containing the ldp:membershipSubject predicate when the membership subject is not the LDPC itself. This triple's object provides clients with the LDPC's membership subject URI.
5.2.5 An LDPC must contain one triple containing the ldp:membershipPredicate or ldp:membershipPredicateInverse predicate when the membership predicate is not rdfs:member.


It says "An LDPC must contain... when the membership subject is not the LDPC itself." and the same for 5.2.5 and rdfs:member .

All I can make of this is that this means "the representation of an LDPC must contain". The default subject is 
defined for the representations returned by the LDPC therefore.

Otherwise things are weird. If a resource somewhere on the web <http://somewhere.com/containers.ttl> 
describes your LDPC  with only one triple such as 

<http://arwe.name/~john/> a ldp:Container .

then what should a client do? Should it determine that because <http://somewhere.com/containers.ttl>
contains no further triples about <http://arwe.name/~john/>, that therefore it should conclude that:

<http://arwe.name/~john/> ldp:membershipSubject <http://arwe.name/~john/>;
          ldp:membershipPredicate rdf:member .

Because if it has to conclude that,  then my argument using the subgraph lemma that I detailed in the 
note in ISSUE-75 http://www.w3.org/2012/ldp/track/issues/75  follows once again. If you then fetched
the <http://arwe.name/~john/> resource and it  returned

<> a ldp:Container;
   ldp:membershipPredicate ex:attachment;
   ldp:membershipSubject <../other> .

then it would seem that <http://somewhere.com/containers.ttl>  which contains a subgraph of 
<http://arwe.name/~john/> leads one to two different and seemingly incompatible 
conclusions.

Henry

> 
> 
> Best Regards, John
> 
> Voice US 845-435-9470  BluePages 
> Tivoli OSLC Lead - Show me the Scenario 
> 
> 

Social Web Architect
http://bblfish.net/
Received on Monday, 3 June 2013 05:12:02 UTC

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