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Re: Duplicate triples Re: RDF Graph

From: Paul Gearon <pag@tucanatech.com>
Date: Sat, 9 Oct 2004 17:21:39 +1000
Message-Id: <DC65A3DB-19C3-11D9-A688-000D93B0E8B6@tucanatech.com>
To: www-rdf-interest@w3.org


On 09/10/2004, at 4:32 PM, Paul Gearon wrote:

> On 07/10/2004, at 7:50 AM, Charles McCathieNevile wrote:
>> On Wed, 6 Oct 2004, Jan Algermissen wrote:
>>> Since the graph is a set it does not contain duplicate triples, yes?
>>
>> I recall a discussion on this topic recently. I believe that someone 
>> who
>> knows the spec better than I do said the formal definition doesn't 
>> prohibit
>> redundant triples, so a conformant program would not necessarily 
>> delete
>> them...
>
> I can't comment on the formal spec on this specific point, as I 
> haven't checked it [1]

OK, I've looked now.  The RDF Semantics document says:
"An RDF graph, or simply a graph, is a set of RDF triples."

This document uses the words "set" and "subset" in a formal sense.  The 
phrase "RDF graph" is linked to the RDF Concepts and Abstract Syntax 
document, which uses semi-formal set algebra to describe its 
definitions.  So when they say "set", they really do seem to mean it.  
Hence, no duplicates.

However, it should be noted that the RDF/XML Syntax spec says:
"Software transforming RDF/XML into a representation of a graph MAY 
eliminate duplicate predicate arcs."

This statement also says that as far as RDF/XML is concerned, duplicate 
statements are not considered significant.  But if you require that 
statements are unique in a graph then you need to check the system you 
are using.

Regards,
Paul Gearon

Software Engineer
Tucana Technologies
http://www.tucanatech.com

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immane mittam.
(Translation from latin: "I have a catapult. Give me all the money,
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Received on Saturday, 9 October 2004 07:22:19 GMT

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