class SPARQL::Algebra::Operator::PathPlus

The SPARQL Property Path `path+` (OneOrMorePath) operator.

@example

(path+ :p)

@see www.w3.org/TR/sparql11-query/#defn_evalPP_OneOrMorePath

Constants

NAME

Public Instance Methods

execute(queryable, **options, &block) click to toggle source

Match on simple relation of subject to object, and then recurse on solutions

@param [RDF::Queryable] queryable

the graph or repository to query

@param [Hash{Symbol => Object}] options

any additional keyword options

@option options [RDF::Term, RDF::Variable] :subject @option options [RDF::Term, RDF::Variable] :object @yield [solution]

each matching solution

@yieldparam [RDF::Query::Solution] solution @yieldreturn [void] ignored @see www.w3.org/TR/sparql11-query/#sparqlAlgebra

# File lib/sparql/algebra/operator/path_plus.rb, line 29
def execute(queryable, **options, &block)
  subject, object = options[:subject], options[:object]
  debug(options) {"Path+ #{[subject, operands, object].to_sse}"}

  # This turns from
  # (:x :p+ ?y)
  # into
  # (:x :p ?y) UNION solutions(:x :p ?y) do |soln|
  #   if :x.variable?
  #     (soln[:x] :p+ soln[:y])
  # end

  # Solutions where predicate exists
  query = if operand.is_a?(RDF::Term)
    RDF::Query.new do |q|
      q.pattern [subject, operand, object]
    end
  else
    operand
  end

  # Block is given on the first invocation, otherwise, results are returned. This is necessary to stop when an existing solution has already been found
  cumulative_solutions = options.fetch(:accumulator, RDF::Query::Solutions.new)

  # Keep track of solutions
  # Recurse into query
  immediate_solutions = []
  queryable.query(query, depth: options[:depth].to_i + 1, **options) do |solution|
    immediate_solutions << solution
  end

  # For all solutions, if they are not in the accumulator, add them and recurse, otherwise skip
  recursive_solutions = RDF::Query::Solutions.new
  immediate_solutions.reject {|s| cumulative_solutions.include?(s)}.each do |solution|
    debug(options) {"(immediate solution)-> #{solution.to_h.to_sse}"}

    # Recurse on subject, if is a variable
    case
    when subject.variable? && object.variable?
      # Query starting with bound object as subject, but replace result with subject
      rs = queryable.query(self, **options.merge(
        subject: solution[object],
        accumulator: (cumulative_solutions + immediate_solutions),
        depth: options[:depth].to_i + 1)).map {|s| s.merge(subject.to_sym => solution[subject])}
      # Query starting with bound subject as object, but replace result with subject
      ro = queryable.query(self, **options.merge(
        object: solution[subject],
        accumulator: (cumulative_solutions + immediate_solutions),
        depth: options[:depth].to_i + 1)).map {|s| s.merge(object.to_sym => solution[object])}
      recursive_solutions += (rs + ro).uniq
    when subject.variable?
      recursive_solutions += queryable.query(self, **options.merge(
        object: solution[subject],
        accumulator: (cumulative_solutions + immediate_solutions),
        depth: options[:depth].to_i + 1)).uniq
    when object.variable?
      recursive_solutions += queryable.query(self, **options.merge(
        subject: solution[object],
        accumulator: (cumulative_solutions + immediate_solutions),
        depth: options[:depth].to_i + 1)).uniq
    end
  end
  debug(options) {"(recursive solutions)-> #{recursive_solutions.map(&:to_h).to_sse}"} unless recursive_solutions.empty?

  solutions = (immediate_solutions + recursive_solutions).uniq
  solutions.each(&block) if block_given? # Only at top-level
  solutions
end