Class: SPARQL::Algebra::Operator::Exists

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

Overview

The SPARQL logical exists operator.

There is a filter operator EXISTS that takes a graph pattern. EXISTS returns true/false depending on whether the pattern matches the dataset given the bindings in the current group graph pattern, the dataset and the active graph at this point in the query evaluation. No additional binding of variables occurs. The NOT EXISTS form translates into fn:not(EXISTS{...}).

[125] ExistsFunc ::= 'EXISTS' GroupGraphPattern

Examples:

SPARQL Grammar

PREFIX :    <http://example/>
SELECT *
WHERE {
  ?set a :Set .
  FILTER EXISTS { ?set :member 9 }
}

SSE

(prefix ((: <http://example/>))
 (filter
  (exists (bgp (triple ?set :member 9)))
  (bgp (triple ?set a :Set))))

See Also:

Constant Summary collapse

NAME = 
[:exists]

Instance Method Summary collapse

Methods included from Evaluatable

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

Instance Method Details

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

Exvaluating this operator executes the query in the first operator passing in each existing bindings.

Parameters:

  • bindings (RDF::Query::Solution) —

    a query solution containing zero or more variable bindings

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

    ({}) options passed from query

  • options[RDF::Queryable] (Hash) —

    a customizable set of options

Returns:

  • (RDF::Literal::Boolean) —

    true or false



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# File 'lib/sparql/algebra/operator/exists.rb', line 40

def evaluate(bindings, **options)
  queryable = options[:queryable]
  !operand(0).execute(queryable, solutions: RDF::Query::Solutions(bindings),
                                 depth: options[:depth].to_i + 1,
                                 **options).empty?
end

#to_sparql(top_level: true, **options) ⇒ String

Returns a partial SPARQL grammar for this operator.

Parameters:

  • top_level (Boolean) (defaults to: true) —

    (true) Treat this as a top-level, generating SELECT ... WHERE {}

Returns:

  • (String) 


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

def to_sparql(top_level: true, **options)
  "EXISTS {\n" +
    operands.last.to_sparql(top_level: false, **options) +
    "\n}"
end