Class: SPARQL::Algebra::Operator::Ask

Inherits:
Unary show all
Includes:
Query
Defined in:
lib/sparql/algebra/operator/ask.rb

Overview

The SPARQL GraphPattern ask operator.

Applications can use the ASK form to test whether or not a query pattern has a solution. No information is returned about the possible query solutions, just whether or not a solution exists.

[12] AskQuery ::= ‘ASK’ DatasetClause* WhereClause ValuesClause

Examples:

SPARQL Query

PREFIX :    <http://example/>
ASK  { :x :p  ?x }

SSE

(prefix ((: <http://example/>))
  (ask
    (bgp (triple :x :p ?x))))

See Also:

Constant Summary collapse

NAME = 
[:ask]

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 included from Query

#solutions

Attributes inherited from SPARQL::Algebra::Operator

#operands

Instance Method Summary collapse

Methods included from Query

#each_solution, #empty?, #failed?, #graph_name=, #matched?, #query_yields_solutions?, #query_yields_statements?, #unshift, #variables

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

#execute(queryable, **options) {|RDF::Literal::Boolean| ... } ⇒ RDF::Literal::Boolean

Executes this query on the given queryable graph or repository. Returns true if any solutions are found, false otherwise.

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

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

    any additional keyword options

Yields:

  • (RDF::Literal::Boolean)

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

Returns:

  • (RDF::Literal::Boolean) —

    \

See Also:



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# File 'lib/sparql/algebra/operator/ask.rb', line 38

def execute(queryable, **options)
  debug(options) {"Ask #{operands.first}"}
  res = boolean(!queryable.query(operands.last, **options.merge(depth: options[:depth].to_i + 1)).empty?)
  yield res if block_given?
  res
end

#query_yields_boolean? ⇒ Boolean

Query results in a boolean result (e.g., ASK)

Returns:

  • (Boolean) 


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# File 'lib/sparql/algebra/operator/ask.rb', line 47

def query_yields_boolean?
  true
end

#to_sparql(**options) ⇒ String

Returns a partial SPARQL grammar for this term.

Returns:

  • (String) 


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

def to_sparql(**options)
  "ASK\n" +
  operands.first.to_sparql(top_level: true, project: nil, **options)
end