class RDF::N3::Algebra::ResourceOperator

This is a generic operator where the subject is a literal or binds to a literal and the object is either a constant that equals the evaluation of the subject, or a variable to which the result is bound in a solution

Constants

NAME

Public Instance Methods

as_literal(object) click to toggle source

Returns a literal for the numeric argument.

# File lib/rdf/n3/algebra/resource_operator.rb, line 111
def as_literal(object)
  case object
  when Float
    literal = RDF::Literal(object, canonicalize: true)
    literal.instance_variable_set(:@string, literal.to_s.downcase)
    literal
  else
    RDF::Literal(object, canonicalize: true)
  end
end
execute(queryable, solutions:, **options) click to toggle source

The operator takes a literal and provides a mechanism for subclasses to operate over (and validate) that argument.

@param [RDF::Queryable] queryable

the graph or repository to query

@param [RDF::Query::Solutions] solutions

solutions for chained queries

@return [RDF::Query::Solutions]

# File lib/rdf/n3/algebra/resource_operator.rb, line 19
def execute(queryable, solutions:, **options)
  RDF::Query::Solutions(solutions.map do |solution|
    subject = operand(0).evaluate(solution.bindings, formulae: formulae) || operand(0)
    object = operand(1).evaluate(solution.bindings, formulae: formulae) || operand(1)
    subject = formulae.fetch(subject, subject) if subject.node?
    object = formulae.fetch(object, object) if object.node?

    log_info(self.class.const_get(:NAME), "subject") {SXP::Generator.string(subject.to_sxp_bin).strip}
    log_info(self.class.const_get(:NAME), "object") {SXP::Generator.string(object.to_sxp_bin).strip}
    next unless valid?(subject, object)

    lhs = resolve(subject, position: :subject)
    if lhs.nil?
      log_error(self.class.const_get(:NAME), "subject evaluates to null") {subject.inspect}
      next
    end

    rhs = resolve(object, position: :object)
    if rhs.nil?
      log_error(self.class.const_get(:NAME), "object evaluates to null") {object.inspect}
      next
    end

    if object.variable?
      log_debug(self.class.const_get(:NAME), "result") {SXP::Generator.string(lhs.to_sxp_bin).strip}
      solution.merge(object.to_sym => lhs)
    elsif subject.variable?
      log_debug(self.class.const_get(:NAME), "result") {SXP::Generator.string(rhs.to_sxp_bin).strip}
      solution.merge(subject.to_sym => rhs)
    elsif respond_to?(:apply)
      res = apply(lhs, rhs)
      log_debug(self.class.const_get(:NAME), "result") {SXP::Generator.string(res.to_sxp_bin).strip}
      # Return the result applying subject and object
      case res
      when RDF::Literal::TRUE
        solution
      when RDF::Literal::FALSE
        nil
      when RDF::Query::Solution
        solution.merge(res)
      else
        log_error(self.class.const_get(:NAME), "unexpected result type")
        nil
      end
    elsif rhs != lhs
      log_debug(self.class.const_get(:NAME), "result: false")
      nil
    else
      log_debug(self.class.const_get(:NAME), "result: true")
      solution
    end
  end.compact.uniq)
end
input_operand() click to toggle source

Input is generically the subject

@return [RDF::Term]

# File lib/rdf/n3/algebra/resource_operator.rb, line 77
def input_operand
  operand(0)
end
resolve(resource, position: :subject) click to toggle source

Subclasses implement ‘resolve`.

Returns nil if resource does not validate, given its position

@param [RDF::Term] resource @return [RDF::Term]

# File lib/rdf/n3/algebra/resource_operator.rb, line 88
def resolve(resource, position: :subject)
  raise NotImplemented
end
valid?(subject, object) click to toggle source

Subclasses may override or supplement validate to perform validation on the list subject

@param [RDF::Term] subject @param [RDF::Term] object @return [Boolean]

# File lib/rdf/n3/algebra/resource_operator.rb, line 98
def valid?(subject, object)
  case subject
  when RDF::Query::Variable
    object.term?
  when RDF::Term
    object.term? || object.variable?
  else
    false
  end
end