Class: SPARQL::Algebra::Operator::Path

Inherits:
Ternary show all
Includes:
Query
Defined in:
lib/sparql/algebra/operator/path.rb

Overview

The SPARQL Property Path path operator.

The second element represents a set of predicates which ar associated with the first (subject) and last (object) operands.

[88] Path ::= PathAlternative

Examples:

SPARQL Grammar

PREFIX :  <http://www.example.org/>
SELECT ?t
WHERE {
  :a :p1|:p2/:p3|:p4 ?t
}

SSE

(prefix ((: <http://www.example.org/>))
 (project (?t)
  (path :a
   (alt
    (alt :p1 (seq :p2 :p3))
    :p4)
   ?t)))

See Also:

Constant Summary collapse

NAME = 
:path

Constants inherited from Ternary

Ternary::ARITY

Constants inherited from SPARQL::Algebra::Operator

ARITY, IsURI, URI

Constants included from Expression

Expression::PATTERN_PARENTS

Instance Attribute Summary

Attributes included from Query

#solutions

Attributes inherited from SPARQL::Algebra::Operator

#operands

Instance Method Summary collapse

Methods included from Query

#each_solution, #empty?, #failed?, #graph_name=, #matched?, #query_yields_boolean?, #query_yields_solutions?, #query_yields_statements?, #unshift, #variables

Methods inherited from Ternary

#initialize

Methods inherited from SPARQL::Algebra::Operator

#aggregate?, arity, #base_uri, base_uri, base_uri=, #bind, #boolean, #constant?, #deep_dup, #each_descendant, #eql?, #evaluatable?, evaluate, #executable?, #first_ancestor, for, #initialize, #inspect, #mergable?, #ndvars, #node?, #operand, #optimize!, #parent, #parent=, #prefixes, prefixes, prefixes=, #rewrite, #to_binary, to_sparql, #to_sxp, #to_sxp_bin, #validate!, #variable?, #variables, #vars

Methods included from Expression

cast, #constant?, #evaluate, extension, extension?, extensions, for, #invalid?, new, #node?, open, #optimize!, parse, register_extension, #to_sxp_bin, #valid?, #validate!, #variable?

Constructor Details

This class inherits a constructor from SPARQL::Algebra::Operator::Ternary

Instance Method Details

#execute(queryable, **options) {|solution| ... } ⇒ RDF::Query::Solutions

Finds solutions from queryable matching the path.

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • options (Hash{Symbol => Object}) —

    any additional keyword options

Yields:

  • (solution) —

    each matching solution

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

Returns:

See Also:



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# File 'lib/sparql/algebra/operator/path.rb', line 46

def execute(queryable, **options, &block)
  debug(options) {"Path #{operands.to_sse}"}
  subject, path_op, object = operands

  @solutions = RDF::Query::Solutions.new
  path_op.execute(queryable,
    subject: subject,
    object: object,
    graph_name: options.fetch(:graph_name, false),
    **options.merge(depth: options[:depth].to_i + 1)
  ) do |solution|
    @solutions << solution
  end
  debug(options) {"=> #{@solutions.inspect}"}
  @solutions.uniq!
  @solutions.each(&block) if block_given?
  @solutions
end

#optimize(**options) ⇒ SPARQL::Algebra::Operator

Special cases for optimizing a path based on its operands.

Parameters:

  • options (Hash{Symbol => Object}) —

    any additional options for optimization

Returns:

See Also:

  • RDF::Query#optimize!


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# File 'lib/sparql/algebra/operator/path.rb', line 85

def optimize(**options)
  op = super
  while true
    decon = op.to_sxp_bin
    op = case decon
    # Reverse
    in [:path, subject, [:reverse, path], object]
      Path.new(object, path, subject)
    # Path* (seq (seq p0 (path* p1)) p2)
    in [:path, subject, [:seq, [:seq, p0, [:'path*', p1]], p2], object]
      pp1 = Variable.new(nil, distinguished: false)
      pp2 = Variable.new(nil, distinguished: false)
      pp3 = Variable.new(nil, distinguished: false)
      # Bind variables used in Path*
      bgp = BGP.new(
        Triple.new(pp2, p2, subject),
        Triple.new(object, p1, pp3))
      # New path with pre-bound variables
      path = Path.new(pp3, PathStar.new(p2), pp2)
      Sequence.new(bgp, path)
    else
      # No matching patterns
      break
    end
  end
  op
end

#to_sparql(top_level: true, **options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Parameters:

  • top_level (Boolean) (defaults to: true) —

    (true) Treat this as a top-level, generating SELECT … WHERE {}

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/path.rb', line 72

def to_sparql(top_level: true, **options)
  str = operands.to_sparql(top_level: false, **options) + " ."
  top_level ? Operator.to_sparql(str, **options) : str
end