Re: [Bigdata-developers] Query projections and multiple VALUES clauses

[Bryan T. <br...@sy...>]

Lee,

These definitely look like bugs.  Can you please file tickets at
http://jira.blazegraph.com and include sample data and expected
solutions for each?  We will try to get the fixes into the 1.5.2
release.

Thanks,
Bryan
----
Bryan Thompson
Chief Scientist & Founder
SYSTAP, LLC
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Greensboro, NC 27410
br...@sy...
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On Wed, May 13, 2015 at 6:51 AM, Lee Kitching <le...@sw...> wrote:
> Hi,
>
> We are trying to migrate our native Sesame database to Blazegraph, however
> we are encountering a problem with the following query which returns no
> results in Blazegraph:
>
> SELECT DISTINCT ?uri WHERE {
>   {
>     SELECT DISTINCT (?uri_d as ?uri) WHERE {
>       VALUES ?type { <http://type1> <http://type2> <http://type3> }
>       VALUES ?dg { <http://graph1> }
>       GRAPH ?dg { ?uri_d a ?type . }
>     }
>   }
>   MINUS
>   {
>     SELECT DISTINCT (?uri_l as ?uri) WHERE {
>     VALUES ?type { <http://type1> <http://type2> <http://type3> }
>     VALUES ?lg { <http://graph2> }
>     GRAPH ?lg { ?uri_l a ?type . }
>     }
>   }
> }
>
> This returns a single result in Sesame since the first subquery returns one
> result and the subquery in the MINUS clause returns none. Executing the
> first subquery
>
> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>   VALUES ?type { <http://type1> <http://type2> <http://type3> }
>   VALUES ?dg { <http://graph1> }
>   GRAPH ?dg { ?uri_d a ?type . }
> }
>
> returns 0 results in Blazegraph, however moving the single graph value into
> the GRAPH clause:
>
> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>   VALUES ?type { <http://type1> <http://type2> <http://type3> }
>   GRAPH <http://graph1> { ?uri_d a ?type . }
> }
>
> returns the expected result. Combining the two VALUES clauses into one:
>
> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>   VALUES (?type ?dg) { (<http://type1> <http://graph1>) (<http://type2>
> <http://graph1>) (<http://type3> <http://graph1>) }
>   GRAPH ?dg { ?uri_d a ?type . }
> }
>
> also returns the result. Does Blazegraph support multiple VALUES clauses in
> the same query? I would expect the three queries above to be equivalent (in
> the case of a single graph).
>
> Another issue is that Blazegraph appears to be inconsistent when projecting
> variables from inner subqueries. The query:
>
> SELECT DISTINCT (?uri_d as ?uri) WHERE {
>   VALUES ?type { <http://type1> <http://type2> <http://type3> }
>   GRAPH <http://graph1> { ?uri_d a ?type . }
> }
>
> returns the expected result, however wrapping this in another projection:
>
> SELECT ?uri WHERE {
>   SELECT (?uri_d as ?uri) WHERE {
>     VALUES ?type { <http://type1> <http://type2> <http://type3> }
>     GRAPH <http://graph1> { ?uri_d a ?type . }
>   }
> }
>
> causes no results to be returned. Surprisingly, projecting an unused
> variable from the inner query:
>
> SELECT ?uri WHERE {
>   SELECT ?type (?uri_d as ?uri) WHERE {
>     VALUES ?type { <http://type1> <http://type2> <http://type3> }
>     GRAPH <http://graph1> { ?uri_d a ?type . }
>   }
> }
>
> causes the result to be returned again.
>
> These two issues appear to be preventing the original MINUS query from
> returning the expected results. Could you confirm these behaviours are bugs?
> I tried looking on the issue tracker but couldn't find anything directly
> related.
>
> Thanks
>
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