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ISSUE: duplicates from UNION

From: Fred Zemke <fred.zemke@oracle.com>
Date: Fri, 22 Sep 2006 14:19:28 -0700
Message-ID: <45145360.9050906@oracle.com>
To: public-rdf-dawg@w3.org

[rq24] 8.2 Union matching - formal definition
The definition is unclear about duplicates.  If S is a solution
of GP1 and S is a solution of GP2, does the solution sequence
contain a copy of S for each of GP1 and GP2?  I believe the
answer should be that duplicates are maintained because they
might be meaningful to the user; if the user wishes to eliminate
duplicates, the user can specify DISTINCT. I think the best
approach would be to recognize that the UNION operator is
constructing a solution sequence from the solution sequences of
each operand.  The proposed rewording is then:

Let P be Pattern1 UNION Pattern2.  Let S1 be a solution sequence 
for Pattern1 and let S2 be a solution sequence for Pattern2.
Then a solution sequence for P is any permutation of 
S1 concatenated with S2.  

Received on Friday, 22 September 2006 21:20:18 UTC

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