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One more question on UNSAID/MINUS

From: Axel Polleres <axel.polleres@urjc.es>
Date: Mon, 11 Dec 2006 09:09:39 +0100
Message-ID: <457D1243.5080401@urjc.es>
To: "Eric Prud'hommeaux" <eric@w3.org>
CC: axel@polleres.net, public-rdf-dawg-comments@w3.org, public-rdf-dawg@w3.org

Eric Prud'hommeaux wrote:
>>* I'd like to suggest to the working group some straightforward 
>>extensions of SPARQL such as adding the set difference operator MINUS, 
>>and allowing nesting of ASK queries in FILTER expressions which come 
>>basically for free in the approach.
> This appears to be an implementation of UNSAID, which the WG has
> decided to phrase as (for example):
>   OPTIONAL { ?x dc:created ?created } .
>   FILTER ( !bound(?created)) }
>   http://www.w3.org/2001/sw/DataAccess/tests/#dawg-unsaid-002
> Please examine the "unsaid" issue description
>   http://www.w3.org/2001/sw/DataAccess/issues#unsaid
> and advise us if you have novel information, or if you are satisfied
> that the WG has discussed these points. You may close this thread by
> responding to this messasge, prefixing the subject with [CLOSED].

Allow me a final question befroe doing so:

As you write it, UNSAID (or MINUS) is already there, "encodable" by 
OPTIONAL and !bound. However, as Jorge's relational algebra shows UNSAID 
should rather be a part of OPTIONAL, i.e. set difference is more down to 
rel. algebra than OPTIONAL, which is then constructible as


It just seems more natural for me to express set difference directly.

best regards,

Dr. Axel Polleres
email: axel@polleres.net  url: http://www.polleres.net/
Received on Monday, 11 December 2006 08:18:59 UTC

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