another problem with Proposal B

• From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
• Date: Thu, 13 Apr 2017 12:50:40 -0700
• To: public-sparql-exists@w3.org
• Message-ID: <0f6eed2f-adf6-f196-6395-e2fe69035bfc@gmail.com>

Proposal B has another problem related to simplification.


The simplification examples in section 18.2.3 of the SPARQL document show that
simplification is to be performed on join(Z,X) for any X.  This removes the
initial empty BGP in many group graph patterns, including
  { VALUES ?junk { } BIND ( ?this AS ?that ) ?that a ex:bad . }
resulting in
  Join( Extend( empty multiset, ?that, ?this ), BGP( ?that a ex:bad ) )
so in
  SELECT ?this WHERE {
    ?this a ex:good .
    FILTER EXISTS { BIND ( ?this AS ?that ) ?that a ex:bad }
    }
solutions will be returned for every direct instance of ex:good if there is
any direct instance of ex:bad, counter to expectations.

peter

Received on Thursday, 13 April 2017 19:51:15 UTC