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Re: blank nodes (once again)

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 16 Mar 2011 21:10:36 -0500
Cc: Ivan Shmakov <oneingray@gmail.com>, Ivan Shmakov <ivan@main.uusia.org>, "semantic-web@w3.org" <semantic-web@w3.org>
Message-Id: <C2B264A5-C107-473C-A900-113FBCCE4C70@ihmc.us>
To: Alan Ruttenberg <alanruttenberg@gmail.com>

On Mar 16, 2011, at 12:30 PM, Alan Ruttenberg wrote:

> Are graph serializations assumed closed world?
> 
> In other words, do graph names act the same way other semantic web names do? 

By 'graph name' you mean, the name of a (named) graph, right? (As opposed to a name used in a graph, ie some random URIref.)  Well, the answer ought to be as defined by the named graph paper that Jeremy and I co-wrote. According to that, the way that a graph name is attached to its graph is like other web identifiers, it is determined by the http protocols. In our current RDF WG terminology, the name URI rigidly denotes the graph which is the g-snap of the g-box which the URI identifies. 

(There is, built into this definition, a presumption or requirement that this g-box is static, i.e. always delivers the same g-text when poked. To handle the more general case, one would need to extend the RDF semantics to a temporal logic framework, with resources that are temporal functions and so on.)

BTW, I wouldn't describe this as 'closed-world'. The correct term might be 'rigid': the name-->named relationship is presumed to hold across all interpretations, when describing the model theory. 

Pat

> 
> -Alan
> 
> On Mar 16, 2011, at 12:34 PM, Pat Hayes <phayes@ihmc.us> wrote:
> 
>> 
>> On Mar 14, 2011, at 11:56 AM, Ivan Shmakov wrote:
>> 
>>>   I guess I'm close to become an annoyance, but I'm going to ask
>>>   yet another blank node question anyway.
>>> 
>>>   Suppose that I have the following graph:
>>> 
>>> :joe :has [ a :dog ]
>>> 
>>>   And suppose that I also have the following one as well:
>>> 
>>> :joe :has [ a :dog ]
>>> 
>>>   From the previous discussion I've learned that there're
>>>   different opinions on whether to consider these graphs, which
>>>   share exactly the same representation, same or different.
>> 
>> The *graphs* may be different, but what they *say* is the same. Each one simply repeats the content of the other one. So you learn nothing new by having both of them rather than one. 
>> 
>> However, that said, according to the current RDF specs, they are also in fact (perhaps two different serializations of) the same graph. Not that this really matters. 
>> 
>>> In
>>>   particular, there's a position that these graphs are different,
>>>   unless they're named the same.  (Somehow, I feel that graph
>>>   naming should be considered tangential to the knowledge it
>>>   represents, but I've noted to myself that there's a different
>>>   opinion.)
>>> 
>>>   But my question is itself tangential to the equivalence of these
>>>   graphs.  Instead, I wonder, if I've assimilated this above
>>>   representation into an RDF store, and going to assimilate its
>>>   exact twin again, does this later assimilation change the
>>>   /knowledge/ contained within such a store, or not?
>> 
>> Not.
>> 
>>> 
>>>   To speak it differently, I've never heard of Joe, and
>>>   (unexpectedly) received a bit of information that speaks: Joe
>>>   has a dog.  Now, I receive another bit, that says exactly the
>>>   same.
>>> 
>>>   I'm quite certain that after I've received the first bit I now
>>>   have a bit more knowledge about the World.  However, I'm not so
>>>   sure that the second bit gives me any more knowledge, since I
>>>   still have no rational means to tell, whether the dog I'm told
>>>   of this time is the same or different to the one about which
>>>   I've already known.
>> 
>> Quite. BTW, this would also be true if you had two graphs with URIs instead of blank nodes, even if they were different URIs. 
>> 
>> :joe :has [:dog1 a :dog]
>> :joe :has [:dog2 a :dog]
>> 
>> You would still not know that the two different *names* for dogs did or did not name the same dog. Maybe (or maybe not) 
>> 
>> :dog1 owl:sameAs :dog2
>> 
>> Pat Hayes
>> 
>>> 
>>>   TIA.
>>> 
>>> -- 
>>> FSF associate member #7257
>> 
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>> 
>> 
>> 
>> 
>> 
>> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
Pensacola                            (850)202 4440   fax
FL 32502                              (850)291 0667   mobile
phayesAT-SIGNihmc.us       http://www.ihmc.us/users/phayes
Received on Thursday, 17 March 2011 02:11:25 UTC

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