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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.

Paul Gearon

Software Engineer
Tucana Technologies

Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum
immane mittam.
(Translation from latin: "I have a catapult. Give me all the money,
or I will fling an enormous rock at your head.")
Received on Saturday, 9 October 2004 07:22:19 UTC

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