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Re: Semantic Web Phase 2 Activity - Protocol - Query Language

From: Steve Harris <S.W.Harris@ecs.soton.ac.uk>
Date: Tue, 11 Nov 2003 17:07:12 +0000
To: www-rdf-interest@w3.org
Message-ID: <20031111170712.GK18188@ecs.soton.ac.uk>

On Tue, Nov 11, 2003 at 05:04:35 +0100, Leo Sauermann wrote:
> because from your answer I think you understood that i wanted to have
> some SQL standard stuff written in the Rdf-Query standard. Like "to
> implement a RDF-Query, you have to use these internal SQL queries" 
> thats not what I meant, the OUTER JOIN problem is a RDF problem you have
> when you try to use RDQL (a very popular query language, imho).
...
> but with today's RDQL this is more complicated:
> if there is no <foaf:image> triple for leo, you don't get any data at
> all.

Yes, agreed, this is a problem. I think that SQL behaviour is a LEFT JOIN
though. I'm not sure how an OUTER JOIN would map to RDQL, but it
would probably give you more rows than that.
http://www.w3schools.com/sql/sql_join.asp

- Steve
Received on Tuesday, 11 November 2003 12:09:28 GMT

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