illustrate basic graph matching conflicts

ACTION: ericP to send mail describing how [VTV] and [BTV] (posted
        [PST]) illustrate basic graph matching conflicts between
        [LC1] and [LC2] semantics
  <http://www.w3.org/2006/09/12-dawg-minutes#action01>
  recorded in http://www.w3.org/2006/09/12-dawg-irc#T14-36-27

In [LC1], basic graph pattern matching was defined in terms of
subgraphs. As I read [LC2],
[[
Definition: Basic Graph Pattern equivalence

Two basic graph patterns are equivalent if there is a bijection M
between the terms of the triple patterns that maps blank nodes to
blank nodes and maps variables, literals and IRIs to themselves, such
that a triple ( s, p, o ) is in the first pattern if and only if the
triple ( M(s), M(p) M(o) ) is in the second.
]]
we have at least an optional leaning. This is supported by the Pellet
demo. For [VTV],
[[
PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT ?who ?type
 WHERE { ?who rdf:type ?type } 
]]
Pellet finds 5 nodes of type foaf:Person. When ?who is projected away,
Pellet reports 1 foaf:Person.

Slightly related:
I was asked by DanC to produce illustrative test cases for all the
design options presented in the draft. I would especially appreciate
help with tests for this issue.

[VTV] http://www.w3.org/2001/sw/DataAccess/tests/#rdfsemantics-var-type-var
[BTV] http://www.w3.org/2001/sw/DataAccess/tests/#rdfsemantics-bnode-type-var
[PST] http://www.w3.org/mid/20060814121827.GC6336@w3.org
[LC1] http://www.w3.org/TR/2005/WD-rdf-sparql-query-20050721/#BasicGraphPatternMatching
[LC2] http://www.w3.org/TR/2006/WD-rdf-sparql-query-20060220/#BasicGraphPatternMatching
-- 
-eric

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