Class: SPARQL::Algebra::Operator::Alt

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

Overview

The SPARQL Property Path alt (Alternative Property Path) operator.

Let P and Q be property path expressions.

eval(Path(X, alt(P,Q), Y)) = Union(eval(Path(X, P, Y)), eval(Path(X, Q, Y)))

[89] PathAlternative ::= PathSequence ( '|' PathSequence )*

Examples:

SPARQL Query

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 = 
:alt

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

Equivalent to:

(path x (alt :p :q) y)
=> (union (bgp (x :p y)) (bgp (x :q y)))

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/alt.rb', line 51

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

  # Solutions where predicate exists
  qa = if operand(0).is_a?(RDF::Term)
    RDF::Query.new do |q|
      q.pattern [subject, operand(0), object]
    end
  else
    operand(0)
  end

  qb = if operand(1).is_a?(RDF::Term)
    RDF::Query.new do |q|
      q.pattern [subject, operand(1), object]
    end
  else
    operand(1)
  end

  query = Union.new(qa, qb)
  queryable.query(query, **options.merge(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/alt.rb', line 81

def to_sparql(**options)
  "(#{operands.first.to_sparql(**options)}|#{operands.last.to_sparql(**options)})"
end