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module SPARQL; module Algebra
class Operator
##
# 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 ')'
#
# @example 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)
# }
#
# @example 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 https://w3c.github.io/rdf-star/rdf-star-cg-spec.html#subject
class Subject < Operator::Unary
include Evaluatable
NAME = :subject
##
# Returns the subject part of arg.
#
# @param [RDF::Statement] operand
# the operand
# @return [RDF::Literal]
# @raise [TypeError] if the operand is not a statement
def apply(operand, **options)
raise TypeError, "expected an RDF::Statement, but got #{operand.inspect}" unless operand.is_a?(RDF::Statement)
operand.subject
end
##
#
# Returns a partial SPARQL grammar for this operator.
#
# @return [String]
def to_sparql(**options)
"SUBJECT(" + operands.last.to_sparql(**options) + ")"
end
end # Subject
end # Operator
end; end # SPARQL::Algebra
Version data entries
8 entries across 8 versions & 1 rubygems