Class: SPARQL::Algebra::Operator::Subject

Inherits:

Operator::Unary

• Object
• Operator::Unary
• SPARQL::Algebra::Operator::Subject

Includes:

Evaluatable

Defined in:

lib/sparql/algebra/operator/subject.rb

Overview

The SPARQL SUBJECT operator.

Returns the subject part of arg as a term.

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

[121] BuiltInCall ::= ... | 'SUBJECT' '(' 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:

• https://w3c.github.io/rdf-star/rdf-star-cg-spec.html#subject

Constant Summary

NAME =

:subject

Instance Method Summary

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

  Returns the subject part of arg.

• #to_sparql(**options) ⇒ String

  Returns a partial SPARQL grammar for this operator.

Methods included from Evaluatable

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

Instance Method Details

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

Returns the subject part of arg.

Parameters:

• operand (RDF::Statement) —

  the operand

Returns:

• (RDF::Literal)

Raises:

• (TypeError) —

  if the operand is not a statement

# File 'lib/sparql/algebra/operator/subject.rb', line 46

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

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Returns:

• (String)

# File 'lib/sparql/algebra/operator/subject.rb', line 56

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