Missing variables in method `to_sparql`

[danielhz]

I tested the following code with sparql 3.2.5:

require 'sparql'

exp = <<-EOS
(extend ((?a1 "a1") (?a2 "a2"))
    (union
     (extend
      ((?a2 "a3") (?a4 "a4"))
      (join (extend
         ((?a5 "a5") (?a6 "a6"))
         (bgp (triple ?s1 ?p1 ?o1) (triple ?s2 ?p2 ?o2) (triple ?s3 ?p3 ?o3)))
        (extend
         ((?a7 "a7") (?a8 "a8"))
         (bgp (triple ?s4 ?p4 ?o4) (triple ?s5 ?p5 ?o5)))))
     (extend ((?a9 "a9") (?a10 "a10")) (bgp (triple ?s6 ?p6 ?o6)))))
EOS

puts SPARQL::Algebra.parse(exp).to_sparql

I expect a query where the variables ?a3 and ?a4. However, in the output listed below, variables ?a3 and ?a4 do not appear.

SELECT *
WHERE {
{
{
{?s1 ?p1 ?o1 . 
?s2 ?p2 ?o2 . 
?s3 ?p3 ?o3 . 

BIND ("a5" AS ?a5) .
BIND ("a6" AS ?a6) .}
{
{?s4 ?p4 ?o4 . 
?s5 ?p5 ?o5 . 

BIND ("a7" AS ?a7) .
BIND ("a8" AS ?a8) .}
}
}
} UNION {
{?s6 ?p6 ?o6 . 

BIND ("a1" AS ?a1) .
BIND ("a2" AS ?a2) .
BIND ("a9" AS ?a9) .
BIND ("a10" AS ?a10) .}
}
BIND ("a1" AS ?a1) .
BIND ("a2" AS ?a2) .
}

[gkellogg]

Generating the query form from the algebra is a bit experimental, and it looks like you've encountered a corner-case. There is a problem in the SSE (((?a2 "a3") (?a4 "a4")) should probably be ((?a3 "a3") (?a4 "a4"))), but I don't even get that far, with an argument error being generated along the way, so there is some mismatch in gem versions resulting in different behavior. Regardless, this shouldn't happen.

I can't promise when I'll be able to look at this in any more detail, as I'm pretty swamped with standards work, and this is challenging code to work with.

[danielhz]

Yes, I intended to write (?e3 "a3"). The same issue occurs if join is replaced with leftjoin.

[danielhz]

I tested the following code with JRuby using the Jena library.

require 'jruby/core_ext'
require 'maven_require'

maven_require 'org.apache.jena:jena-core'
maven_require 'org.apache.jena:jena-arq'
maven_require 'org.apache.logging.log4j:log4j-api'
maven_require 'org.apache.logging.log4j:log4j-core'
maven_require 'org.apache.logging.log4j:log4j-slf4j-impl'

java_import 'org.apache.jena.sys.JenaSystem'
java_import 'org.apache.jena.sparql.algebra.Algebra'
java_import 'org.apache.jena.sparql.algebra.OpAsQuery'

JenaSystem.init

exp = <<-EOS
(extend ((?a1 "a1") (?a2 "a2"))
    (union
     (extend
      ((?a2 "a3") (?a4 "a4"))
      (join (extend
         ((?a5 "a5") (?a6 "a6"))
         (bgp (triple ?s1 ?p1 ?o1) (triple ?s2 ?p2 ?o2) (triple ?s3 ?p3 ?o3)))
        (extend
         ((?a7 "a7") (?a8 "a8"))
         (bgp (triple ?s4 ?p4 ?o4) (triple ?s5 ?p5 ?o5)))))
     (extend ((?a9 "a9") (?a10 "a10")) (bgp (triple ?s6 ?p6 ?o6)))))
EOS

ops = Algebra.parse(exp)
puts OpAsQuery.as_query(ops).to_s

The output is the following:

SELECT  *
WHERE
  {   { { { ?s1  ?p1  ?o1 .
            ?s2  ?p2  ?o2 .
            ?s3  ?p3  ?o3
            BIND("a5" AS ?a5)
            BIND("a6" AS ?a6)
          }
          { ?s4  ?p4  ?o4 .
            ?s5  ?p5  ?o5
            BIND("a7" AS ?a7)
            BIND("a8" AS ?a8)
          }
        }
        BIND("a3" AS ?a2)
        BIND("a4" AS ?a4)
      }
    UNION
      { ?s6  ?p6  ?o6
        BIND("a9" AS ?a9)
        BIND("a10" AS ?a10)
      }
    BIND("a1" AS ?a1)
    BIND("a2" AS ?a2)
  }