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

Inherits:
Unary 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

Constants inherited from Unary

Unary::ARITY

Constants inherited from SPARQL::Algebra::Operator

ARITY, IsURI, URI

Constants included from Expression

Expression::PATTERN_PARENTS

Instance Attribute Summary

Attributes inherited from SPARQL::Algebra::Operator

#operands

Instance Method Summary collapse

Methods included from Evaluatable

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

Methods inherited from Unary

#initialize

Methods inherited from SPARQL::Algebra::Operator

#aggregate?, arity, #base_uri, base_uri, base_uri=, #bind, #boolean, #constant?, #deep_dup, #each_descendant, #eql?, #evaluatable?, evaluate, #executable?, #first_ancestor, for, #initialize, #inspect, #ndvars, #node?, #operand, #optimize, #optimize!, #parent, #parent=, #prefixes, prefixes, prefixes=, #rewrite, #to_binary, to_sparql, #to_sxp, #to_sxp_bin, #validate!, #variable?, #variables, #vars

Methods included from Expression

cast, #constant?, #evaluate, extension, extension?, extensions, for, #invalid?, new, #node?, open, #optimize, #optimize!, parse, register_extension, #to_sxp_bin, #valid?, #validate!, #variable?

Constructor Details

This class inherits a constructor from SPARQL::Algebra::Operator::Unary

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