W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > July to September 2009

Algebra expression for MINUS

From: Simon Schenk <sschenk@uni-koblenz.de>
Date: Wed, 08 Jul 2009 16:31:59 +0000
To: "public-rdf-dawg@w3.org" <public-rdf-dawg@w3.org>
Message-Id: <1247070719.18947.31.camel@tweety>

I've been fiddling with algebra expressions for MINUS and I am wondering
whether the following capture the semantics of antijoin with restriction
to shared variables:

A \ (A |X| [Projection to vars in A] B)

If A and B do not share a variable, the projection results in a relation
with zero colums. I am not sure, whether this is even defined. 

Does anyone of the relational algebra gurus out there have a clue?


Simon Schenk | ISWeb | Uni Koblenz
Five sentences policy: http://five.sentenc.es/

Received on Wednesday, 8 July 2009 16:32:40 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 7 January 2015 15:00:57 UTC