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Re: a blank node issue

From: Pat Hayes <phayes@ihmc.us>
Date: Wed, 2 Mar 2011 13:52:54 -0600
Cc: Reto Bachmann-Gmür <reto.bachmann@trialox.org>, Richard Cyganiak <richard@cyganiak.de>, William Waites <ww@styx.org>, nathan@webr3.org, Ivan Shmakov <oneingray@gmail.com>, semantic-web@w3.org
Message-Id: <716A180B-3AD0-4DBE-8FAB-04984AD26533@ihmc.us>
To: Jiří Procházka <ojirio@gmail.com>

On Mar 2, 2011, at 1:17 PM, Jiří Procházka wrote:

> On 03/02/2011 07:50 PM, Reto Bachmann-Gmür wrote:
>> ----- Original message -----
>>> On 03/02/2011 07:21 PM, Pat Hayes wrote:
>>>> 
>>>> On Mar 2, 2011, at 9:54 AM, Richard Cyganiak wrote:
>>>> 
>>>>> On 2 Mar 2011, at 14:18, William Waites wrote:
>>>>>> maybe some convention or
>>>>>> standard for skolemising blank nodes so they can be 
>>>>>> referred to might be a good thing?
>>>>> 
>>>>> There is already a convention/standard for skolemising blank nodes:
>>>>> just use a URI instead.
>>>> 
>>>> But that subtly changes the RDF, because the URI has global scope. 
>>> 
>>> Is there any practical difference between bnodes and normal nodes,
>>> except the scope (and necessity) of their name?
>> 
>> Yes, a graph with bnodes can potentially be simplified: the same meaning may be expressed with a more lean graph, i.e. with less nodes and triples. If all your nodes are uris you cannot do simplifications with rdf entaillment.
> 
> So that in fact means that bnodes are considered from a closed world
> scenario, where we assume there are no other references to the node
> outside of what we know.

Um... yes, but please don't use the phrase 'closed world' which means something rather different. Bnodes have local scope, a syntactic issue rather than a semantic one. 

> On the other hand normal nodes have global
> identifier which forces us to consider it from an open world scenario.

LIkewise, 'global scope' rather than 'open world', please. Thanks.  But yes, what you say is correct. 

> 
> To the scoping of the blank nodes: doesn't anyone else think there
> should be several types of blank nodes? (example: current graph, current
> document, maybe even specific document)

We need to get the scope rule(s) clarified, for sure. (More on this topic later.) Maybe we need several kinds of scope, but I hope not. But please lets not code this by having many kinds of node :-((

Pat

> 
> Best,
> Jiri
> 
>> Cheers,
>> Reto
>> 
>>> 
>>> Best,
>>> Jiri
>>> 
>>>> Pat
>>>> 
>>>>> 
>>>>> Richard
>>>>> 
>>>>> 
>>>>>> 
>>>>>> Cheers,
>>>>>> -w
>>>>>> -- 
>>>>>> William Waites                               <mailto:ww@styx.org>
>>>>>> http://river.styx.org/ww/               <sip:ww@styx.org>
>>>>>> F4B3 39BF E775 CF42 0BAB   3DF0 BE40 A6DF B06F FD45
>>>>>> 
>>>>> 
>>>>> 
>>>> 
>>>> ------------------------------------------------------------
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>>>> 3973       40 South Alcaniz St.                     (850)202 4416     office
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>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>> 
>> 
> 

------------------------------------------------------------
IHMC                                     (850)434 8903 or (650)494 3973   
40 South Alcaniz St.           (850)202 4416   office
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Received on Wednesday, 2 March 2011 19:54:00 UTC

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