Class: RDF::N3::Algebra::ResourceOperator

Inherits:
SPARQL::Algebra::Operator::Binary
  • Object
show all
Includes:
Builtin, SPARQL::Algebra::Query, SPARQL::Algebra::Update
Defined in:
lib/rdf/n3/algebra/resource_operator.rb

Overview

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

Constant Summary collapse

NAME = 
:resourceOperator

Instance Attribute Summary

Attributes included from Enumerable

#existentials, #universals

Instance Method Summary collapse

Methods included from Builtin

#each, #evaluate, #hash, #rank, #to_uri

Instance Method Details

#as_literal(object) ⇒ Object

Returns a literal for the numeric argument.



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# 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) ⇒ RDF::Query::Solutions

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

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • solutions (RDF::Query::Solutions) —

    solutions for chained queries

Returns:

  • (RDF::Query::Solutions) 


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# 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 ⇒ RDF::Term

Input is generically the subject

Returns:



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# File 'lib/rdf/n3/algebra/resource_operator.rb', line 77

def input_operand
  operand(0)
end

#resolve(resource, position: :subject) ⇒ RDF::Term

Subclasses implement resolve.

Returns nil if resource does not validate, given its position

Parameters:

Returns:

Raises:



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# File 'lib/rdf/n3/algebra/resource_operator.rb', line 88

def resolve(resource, position: :subject)
  raise NotImplemented
end

#valid?(subject, object) ⇒ Boolean

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

Parameters:

Returns:

  • (Boolean) 


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# 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