Class: SPARQL::Algebra::Operator::Bound

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

Overview

The SPARQL bound operator.

[121] BuiltInCall ::= ... | 'BOUND' '(' Var ')'

Examples:

SPARQL Grammar

PREFIX  : <http://example.org/ns#>
SELECT  ?a ?c
WHERE
    { ?a :b ?c . 
      OPTIONAL
        { ?c :d ?e } . 
      FILTER (! bound(?e)) 
    }

SSE

(prefix ((: <http://example.org/ns#>))
  (project (?a ?c)
    (filter (! (bound ?e))
      (leftjoin
        (bgp (triple ?a :b ?c))
        (bgp (triple ?c :d ?e))))))

See Also:

Constant Summary collapse

NAME = 
:bound

Instance Method Summary collapse

Methods included from Evaluatable

#apply, #memoize, #replace_aggregate!, #replace_vars!

Constructor Details

#initialize(var, **options) ⇒ Bound

Initializes a new operator instance.

Parameters:

Raises:

  • (TypeError) —

    if any operand is invalid



40
41
42
 
# File 'lib/sparql/algebra/operator/bound.rb', line 40

def initialize(var, **options)
  super
end

Instance Method Details

#evaluate(bindings, **options) ⇒ RDF::Literal::Boolean

Returns true if var is bound to a value. Returns false otherwise. Variables with the value NaN or INF are considered bound.

Parameters:

  • bindings (RDF::Query::Solution) —

    a query solution containing zero or more variable bindings

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

    ({}) options passed from query

Returns:

  • (RDF::Literal::Boolean) —

    true or false

Raises:

  • (TypeError) —

    if the operand is not a variable



53
54
55
56
57
58
59
60
 
# File 'lib/sparql/algebra/operator/bound.rb', line 53

def evaluate(bindings, **options)
  case var = operand
    when Variable
      bindings.respond_to?(:bound?) && bindings.bound?(var) ?
        RDF::Literal::TRUE : RDF::Literal::FALSE
    else raise TypeError, "expected an RDF::Query::Variable, but got #{var.inspect}"
  end
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


67
68
69
 
# File 'lib/sparql/algebra/operator/bound.rb', line 67

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