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Re: Re: why arcs never be merged?

From: Jeff Zhang <jeffzhang726@yahoo.com.cn>
Date: Fri, 29 Nov 2002 21:50:41 -0800
Message-Id: <200211291345.IAA24464@tux.w3.org>
To: Graham Klyne <GK@ninebynine.org>
CC: "www-rdf-interest@w3.org" <www-rdf-interest@w3.org>

Dear Graham,
 I mean the first example
    ex:foo ex:property ex:bar .
and                            
    ex:foo ex:property ex:bar .
    ex:foo ex:property ex:bar .

Our team is developping an rdf engine which has an API as its part.
When we discuss about the operation of adding a statement to a graph, we are puzzled
about whether a statement should be added to the graph if there is already a same 
statement in the graph. As to the rule of merging graphs, it seems the same statement should be added to the graph. But we can not find any real world example in which multiple copies of statements make different meanings with single statement. Is there any example?

	

======= 2002-11-29 12:26:00 =======

>At 12:02 PM 11/29/02 -0800, JeffZhang wrote:
>
>>Dear all,
>>   When two graphs merged, arcs are never merged,why? What the difference 
>> between a single
>>assertion and duplicated assertions?
>
>Do you mean the distinction between these graphs:
>
>    ex:foo ex:property ex:bar .
>
>and
>
>    ex:foo ex:property ex:bar .
>    ex:foo ex:property ex:bar .
>
>?
>
>Semantically, they are the same in that each entails the other.  How they 
>are treated syntactically is rather up to an application.
>
>
>Or do you mean:
>
>    ex:foo ex:property ex:bar .
>    ex:foo ex:property ex:bif .
>
>?
>
>These are two distinct statements -- what would it mean to merge the 
>arcs?  Each arc is, in effect, the combination of subject, object and 
>predicate:  no arc exists separately from a statement.  The URI that labels 
>an arc may, however, be a separate node in the graph, and the presence of 
>multiple arcs with a given URI don't mean that the URI node can appear 
>multiple times.
>
>A slightly different way of looking at this is that the property URI is a 
>kind of type label, and an arc is an instance of that type.
>
>>   The literals,which were not merged in previous specificaions, are 
>> merged in this version.
>
>That's down to a semantic change in the nature of literals, a big 
>discussion quite different from the matter of arcs.
>
>>Would the same change happen to arcs?
>
>There is no discussion that I've heard that calls to change the role of arcs.
>
>#g
>
>
>-------------------
>Graham Klyne
><GK@NineByNine.org>

= = = = = = = = = = = = = = = = = = = =
			

Best regards,        

Jeff Zhang
jeffzhang726@yahoo.com.cn
2002-11-29



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Received on Friday, 29 November 2002 08:45:59 GMT

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