Re: Issue 1 - ToMultiSet

good morning;

> On 2016-07-07, at 11:27, Andy Seaborne <andy@apache.org> wrote:
> 
> On the first point:
> 
> [[
> Problem 1: Some uses of EXISTS are undefined
> 
> exists is only defined for graph patterns, but in
> SELECT ?x WHERE {
> ?x :p :c .
> FILTER EXISTS { SELECT ?y { ?y :q :c . } } }
> the argument to exists ends up being a ToMultiSet, which is not listed under "Graph Pattern" in the table of SPARQL algebra symbols.
> ]]
> 
> This isn't specific to EXISTS. It's about anywhere a sub-SELECT is used.  { ... } is a graph pattern group and results in a join. The arguments to join are teh evaluation of a graph patterns - multisets.
> 
> Looking at it use in "18.2.2.6 Translate Graph Patterns [1] (right at the end of the section), the last example of "18.2.3 Examples of Mapped Graph Patterns" [2] and "18.2.4.3 VALUES" [3], using is join shows it in the same light as the other graph patterns.
> 
> Therefore, I think we can address this with an entry in the https://www.w3.org/2013/sparql-errata
> 
> Draft:
> 
> [[
> query-errata-N:
> 
> "Section 18.2 Translation to the SPARQL Algebra" intro (end):
> 
> ToMultiSet can be used where a graph pattern is mentioned below because
> the outcome of evaluating a graph pattern is a multiset.
> ]]
> 
> ToMultiSet has the same result type the same as the other graph patterns but it is also a solution modifier (acts on a solution sequence).
> 
>    Andy
> 
> 
> [1]
> https://www.w3.org/TR/sparql11-query/#sparqlTranslateGraphPatterns
> [2]
> https://www.w3.org/TR/sparql11-query/#sparqlAlgebraExamples
> [3]
> https://www.w3.org/TR/sparql11-query/#sparqlAlgebraFinalValues
> 

-1

if the issue is that, as per 18.6, the exists definition is in terms of the symbols specified in the 18.2 abstract algebra table for “graph pattern”, [125,125]->[53] permit a subselect, and 18.2.2.6 indicates that a subselect is rewritten to a ToMultiset, but ToMultiset is missing in the 18.2 table, rather than to reiterate in a note something which already follows from the algebra - as described above, it would be more specific and easier to follow, to either
- extend the 18.2 table, or
- change the definition of exists itself to permit as arguments those abstract forms which the operator is to combine.

.best regards, from berlin,
---
james anderson | james@dydra.com | http://dydra.com