Class: SPARQL::Algebra::Operator::Predicate

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

Overview

The SPARQL PREDICATE operator.

If triple is an RDF-star triple, the function returns the predicate of this triple. Passing anything other than an RDF-star triple is an error.

[121] BuiltInCall ::= ... | 'PREDICATE' '(' Expression ')'

Examples:

SPARQL Grammar

PREFIX : <http://example.com/ns#>
SELECT * {
  ?t :source :g
  FILTER(isTriple(?t))
  FILTER(SUBJECT(?t) = :s)
  FILTER(PREDICATE(?t) = :p)
  FILTER(OBJECT(?t) = :o)
}

SSE

(prefix
 ((: <http://example.com/ns#>))
 (filter
  (exprlist
   (isTRIPLE ?t)
   (= (subject ?t) :s)
   (= (predicate ?t) :p)
   (= (object ?t) :o))
  (bgp (triple ?t :source :g))) )

See Also:

Constant Summary collapse

NAME = 
:predicate

Instance Method Summary collapse

Methods included from Evaluatable

#evaluate, #memoize, #replace_aggregate!, #replace_vars!

Instance Method Details

#apply(operand, **options) ⇒ RDF::Literal

Returns the predicate part of arg.

Parameters:

Returns:

  • (RDF::Literal)

Raises:

  • (TypeError) —

    if the operand is not a statement



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# File 'lib/sparql/algebra/operator/predicate.rb', line 44

def apply(operand, **options)
  raise TypeError, "expected an RDF::Statement, but got #{operand.inspect}" unless operand.is_a?(RDF::Statement)
  operand.predicate
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

  • (String) 


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# File 'lib/sparql/algebra/operator/predicate.rb', line 54

def to_sparql(**options)
  "PREDICATE(" + operands.last.to_sparql(**options) + ")"
end