NoMethodError: undefined method `execute' for #<Array:0x007fb6e33c3380>

[mwkuster]

The following program snippet produces the following stack trace: NoMethodError: undefined method execute' for #<Array:0x007fb6e33c3380> from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sparql-1.0.7/lib/sparql/algebra/operator/extend.rb:35:inexecute' from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sparql-1.0.7/lib/sparql/algebra/operator/project.rb:30:in execute' from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sparql-1.0.7/lib/sparql/algebra/operator/distinct.rb:32:inexecute' from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sparql-1.0.7/lib/sparql/algebra/operator/prefix.rb:30:in execute' from /opt/local/lib/ruby1.9/gems/1.9.1/gems/sparql-1.0.7/lib/sparql.rb:85:inexecute' from (irb):12 from /opt/local/bin/irb1.9:12:in `

'

Again, the query validates against http://www.sparql.org/validate/query and produces the following output with ARQ:

?number: "2010/24 (EU)"^^http://www.w3.org/2001/XMLSchema#string ?typedoc "DIR"^^http://www.w3.org/2001/XMLSchema#string ?is_corrigendum "O"^^http://www.w3.org/2001/XMLSchema#string ?langs "fra-eng"

---

require 'rdf' require 'rdf/turtle' rep = RDF::Repository.new rep.load("https://raw.github.com/mwkuster/eli-budabe/master/sparql/source.ttl") query = "PREFIX cdm: http://publications.europa.eu/ontology/cdm#\n\nSELECT DISTINCT ?number ?typedoc ?is_corrigendum (GROUP_CONCAT(?lang_code; separator=\"-\") AS ?langs)\nWHERE\n{\n ?manif cdm:manifestation_official-journal_part_information_number ?number .\n ?manif cdm:manifestation_official-journal_part_typedoc_printer ?typedoc .\n ?manif cdm:manifestation_official-journal_part_is_corrigendum_printer ?is_corrigendum .\n ?manif cdm:manifestation_manifests_expression ?expr .\n ?expr cdm:expression_uses_language ?lang .\n BIND(lcase(replace(str(?lang), \".*/([A-Z]{3})\", \"$1\")) AS ?lang_code)\n}\nGROUP BY ?number ?typedoc ?is_corrigendum\n" require 'sparql' s = SPARQL.execute(query, rep)

[gkellogg]

Most likely, this is because your invoking an algebra operator which hasn't yet been implemented. I'll at least see if I can get a better error message out.

[mwkuster]

Which operator would then be the culprit? Seems that you support group_concat?

[gkellogg]

No, group operations aren't supported yet, although concat is. This query uses GROUP. The corrected query is:

PREFIX cdm: <http://publications.europa.eu/ontology/cdm#>

SELECT DISTINCT ?number ?typedoc ?is_corrigendum (GROUP_CONCAT(?lang_code; separator="-") AS ?langs)
WHERE
{
 ?manif cdm:manifestation_official-journal_part_information_number ?number .
 ?manif cdm:manifestation_official-journal_part_typedoc_printer ?typedoc .
 ?manif cdm:manifestation_official-journal_part_is_corrigendum_printer ?is_corrigendum .
 ?manif cdm:manifestation_manifests_expression ?expr .
 ?expr cdm:expression_uses_language ?lang .
 BIND(lcase(replace(str(?lang), ".*/([A-Z]{3})", "$1")) AS ?lang_code)
}
GROUP BY ?number ?typedoc ?is_corrigendum

Which generates the (possibly incorrect) algebra:

(prefix
 ((cdm: <http://publications.europa.eu/ontology/cdm#>))
 (distinct
  (project
   (?number ?typedoc ?is_corrigendum ?langs)
   (extend
    ((?langs (group_concat (separator "-") ?lang_code)))
    (group
     (?number ?typedoc ?is_corrigendum)
     (extend
      ((?lang_code (lcase (replace (str ?lang) ".*/([A-Z]{3})" "$1"))))
      (bgp
       (triple ?manif cdm:manifestation_official-journal_part_information_number ?number)
       (triple ?manif cdm:manifestation_official-journal_part_typedoc_printer ?typedoc)
       (triple ?manif
        cdm:manifestation_official-journal_part_is_corrigendum_printer
        ?is_corrigendum )
       (triple ?manif cdm:manifestation_manifests_expression ?expr)
       (triple ?expr cdm:expression_uses_language ?lang)) )) )) ))

There are some subtleties to aggregating bind variables when doing groups and I need time to focus on. Because the (group) operator isn't implemented, it is rendered as an array such as [:group, [?number ?typedoc ..] ...]. We try to execute this, and it fails. This can be addressed by having Array#execute raise a NotImplemented error, and reference the operator name. I'll do this after I've completed the support for custom functions, which is pretty close.

[mwkuster]

With the help of your excellent explanation I've rewritten the query to an alternative version using a subquery:

PREFIX cdm: http://publications.europa.eu/ontology/cdm#

SELECT DISTINCT ?number ?typedoc ?is_corrigendum ?langs WHERE { ?manif cdm:manifestation_official-journal_part_information_number ?number . ?manif cdm:manifestation_official-journal_part_typedoc_printer ?typedoc . ?manif cdm:manifestation_official-journal_part_is_corrigendum_printer ?is_corrigendum . { SELECT DISTINCT (GROUP_CONCAT(?lang_code; separator="-") AS ?langs) WHERE { ?expr cdm:expression_uses_language ?lang . BIND(lcase(replace(str(?lang), ".*/([A-Z]{3})", "$1")) AS ?lang_code) } } }

Now, it does not produce an error and correctly returns ?number, ?typedoc and ?is_corrigendum, but ?langs is also not bound

[mwkuster]

P. S.: In my case there is an easy workaround to this, i.e. to split this query into two separate ones and use application logic to merge them.

[gkellogg]

Pushed in version 1.0.8.