Class: SPARQL::Algebra::Operator::Describe

Inherits:
Operator::Binary
  • Object
show all
Includes:
Query
Defined in:
lib/sparql/algebra/operator/describe.rb

Overview

The SPARQL GraphPattern describe operator.

Generages a graph across specified terms using RDF::Queryable#concise_bounded_description.

[11] DescribeQuery ::= 'DESCRIBE' ( VarOrIri+ | '' ) DatasetClause WhereClause? SolutionModifier ValuesClause

Examples:

SPARQL Grammar

BASE <http://example.org/>
DESCRIBE <u> ?u WHERE { <x> <q> ?u . }

SSE

(base <http://example.org/>
 (describe (<u> ?u)
  (bgp (triple <x> <q> ?u))))

See Also:

Constant Summary collapse

NAME = 
[:describe]

Instance Attribute Summary

Attributes included from Query

#solutions

Instance Method Summary collapse

Methods included from Query

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

Instance Method Details

#execute(queryable, **options) {|statement| ... } ⇒ RDF::Graph

Executes this query on the given RDF::Queryable object. Generates a graph containing the Concise Bounded Description variables and URIs listed in the first operand.

Examples:

(describe (<http://example/>))
(prefix ((foaf: <http://xmlns.com/foaf/0.1/>))
  (describe (?x)
    (bgp (triple ?x foaf:mbox <mailto:alice@org>))))

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

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

    any additional keyword options

Yields:

  • (statement) —

    each matching statement

Yield Parameters:

Yield Returns:

  • (void) —

    ignored

Returns:

  • (RDF::Graph) —

    containing the constructed triples

See Also:



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# File 'lib/sparql/algebra/operator/describe.rb', line 49

def execute(queryable, **options, &block)
  debug(options) {"Describe #{operands.first}, #{options.inspect}"}

  # Describe any constand URIs
  to_describe = operands.first.select {|t| t.uri?}
  
  to_describe.each {|t| debug(options) {"=> describe #{t}"}}

  queryable.query(operands.last) do |solution|
    solution.each_variable do |v|
      if operands.first.any? {|bound| v.eql?(bound)}
        debug(options) {"(describe)=> #{v}"}
        to_describe << v.value
      end
    end
  end

  # Return Concise Bounded Description
  queryable.concise_bounded_description(*to_describe.uniq, &block)
end

#query_yields_statements? ⇒ Boolean

Query results statements (e.g., CONSTRUCT, DESCRIBE, CREATE)

Returns:

  • (Boolean) 


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# File 'lib/sparql/algebra/operator/describe.rb', line 72

def query_yields_statements?
  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/describe.rb', line 81

def to_sparql(**options)
  str = "DESCRIBE "
  str << if operands[0].empty?
    "*"
  else
    operands[0].map { |e| e.to_sparql(**options) }.join(" ")
  end

  str << "\n"
  str << operands[1].to_sparql(top_level: true, project: nil, **options)
end