Class: SPARQL::Algebra::Operator::Reverse

Inherits:
Operator::Unary
  • Object
show all
Includes:
Query
Defined in:
lib/sparql/algebra/operator/reverse.rb

Overview

The SPARQL Property Path reverse (NegatedPropertySet) operator.

[92] PathEltOrInverse ::= PathElt | '^' PathElt

Examples:

SPARQL Grammar

PREFIX ex:	<http://www.example.org/schema#>
PREFIX in:	<http://www.example.org/instance#>
ASK { in:b ^ex:p in:a }

SSE

(prefix ((ex: <http://www.example.org/schema#>)
         (in: <http://www.example.org/instance#>))
 (ask (path in:b (reverse ex:p) in:a)))

SPARQL Grammar

prefix ex:	<http://www.example.org/schema#>
prefix in:	<http://www.example.org/instance#>

select  * where { in:c ^(ex:p1/ex:p2) ?x }

SSE

(prefix ((ex: <http://www.example.org/schema#>)
         (in: <http://www.example.org/instance#>))
 (path in:c (reverse (seq ex:p1 ex:p2)) ?x))

See Also:

Constant Summary collapse

NAME = 
:reverse

Instance Attribute Summary

Attributes included from Query

#solutions

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

Instance Method Details

#execute(queryable, **options) {|solution| ... } ⇒ Object

Equivliant to:

(path (:a (reverse :p) :b))
=> (bgp (:b :p :a))

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

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

    any additional keyword options

Options Hash (**options):

Yields:

  • (solution) —

    each matching solution

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

See Also:



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# File 'lib/sparql/algebra/operator/reverse.rb', line 53

def execute(queryable, **options, &block)
  debug(options) {"Reverse #{operands.to_sse}"}
  subject, object = options[:subject], options[:object]

  # Solutions where predicate exists
  query = if operand.is_a?(RDF::Term)
    RDF::Query.new do |q|
      q.pattern [object, operand, subject]
    end
  else
    operand(0)
  end
  queryable.query(query, **options.merge(
    subject: object,
    object: subject,
    depth: options[:depth].to_i + 1
  ), &block)

end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/reverse.rb', line 78

def to_sparql(**options)
  "^(" + operands.first.to_sparql(**options) + ')'
end