proposed erratum for SPARQL 1.1 Query Language concerning categorization of multisets of solution mappings

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proposed erratum for SPARQL 1.1 Query Language concerning categorization of multisets of solution mappings

Peter F. Patel-Schneider
Add to Section 18.2 after the table of symbols in the SPARQL alebra:

  A multiset of solution mappings is a element of the SPARQL algebra and is a
  Graph Pattern.

Rationale:  The mapping of VALUES constructs are multisets of symbol
mappings but are not currently listed as elements of the SPARQL algebra,
potentially resulting in confusion as to how they are to be handled.

Effect: This change eliminates a potential problem in the definition of the
exists function where its argument is a multiset and thus arguably not a
"graph pattern".  This situation occurs in
  SELECT ?x WHERE {
    ?x :p :c .
    FILTER NOT EXISTS { VALUES ?y { :d } }
  }

The example doesn't make much sense but has been chosen to not exhibit any
cases where EXISTS is otherwise problematic.


Peter F. Patel-Schneider
Nuance Communications