Class: RDF::Query::Pattern

Inherits:
Statement show all
Defined in:
vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb,
vendor/bundler/ruby/2.0.0/bundler/gems/sparql-da60321cd7bc/lib/sparql/algebra/extensions.rb

Overview

An RDF query pattern.

Since:

Instance Attribute Summary (collapse)

Attributes inherited from Statement

#context, #id, #object, #predicate, #subject

Instance Method Summary (collapse)

Methods inherited from Statement

#==, #===, #[], #[]=, #asserted?, #eql?, #has_blank_nodes?, #has_context?, #has_graph?, #has_object?, #has_predicate?, #has_subject?, #inferred?, #invalid?, #quoted?, #reified, #statement?, #to_hash, #to_quad, #to_triple, #valid?, #variable?

Methods included from Value

#anonymous?, #constant?, #graph?, #inspect, #inspect!, #invalid?, #iri?, #list?, #literal?, #node?, #resource?, #statement?, #term?, #to_nquads, #to_ntriples, #to_rdf, #type_error, #uri?, #valid?, #validate!, #variable?

Constructor Details

- (Pattern) initialize(options = {}) - (Pattern) initialize(subject, predicate, object, options = {})

A new instance of Pattern

Overloads:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 35

def initialize(subject = nil, predicate = nil, object = nil, options = {})
  super
end

Instance Attribute Details

- (Numeric) cost

The estimated cost of this pattern (for query optimization).

Returns:

  • (Numeric) 


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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 59

def cost
  @cost
end

- (Hash) options (readonly)

Any additional options for this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 53

def options
  @options
end

Instance Method Details

- (Integer) binding_count

Returns the number of bindings in this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 243

def binding_count
  bindings.size
end

- (Hash{Symbol => RDF::Term}) bindings

Returns all bindings in this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 251

def bindings
  bindings = {}
  bindings.merge!(subject.bindings)   if subject.is_a?(Variable)
  bindings.merge!(predicate.bindings) if predicate.is_a?(Variable)
  bindings.merge!(object.bindings)    if object.is_a?(Variable)
  bindings.merge!(context.bindings)   if context.is_a?(Variable)
  bindings
end

- (Boolean) bindings?

Returns true if this pattern contains bindings.

Returns:

  • (Boolean) —

    true or false



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 235

def bindings?
  !bindings.empty?
end

- (Boolean) blank?

Returns true if this is a blank pattern, with all terms being nil.

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 66

def blank?
  subject.nil? && predicate.nil? && object.nil? && context.nil?
end

- (Boolean) bound?

Returns true if all variables in this pattern are bound.

Returns:

  • (Boolean) —

    true or false



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 264

def bound?
  !variables.empty? && variables.values.all?(&:bound?)
end

- (Hash{Symbol => Variable}) bound_variables

Returns all bound variables in this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 272

def bound_variables
  variables.reject { |name, variable| variable.unbound? }
end

- (Enumerator) execute(queryable, bindings = {}) {|statement| ... }

Executes this query pattern on the given queryable object.

Values are matched using using Queryable#query_pattern.

If the optional bindings are given, variables will be substituted with their values when executing the query.

To match triples only in the default context, set context to false.

Examples:

Pattern.new(:s, :p, :o).execute(RDF::Repository.load('etc/doap.nt'))

Parameters:

Yields:

  • (statement) —

    each matching statement

Yield Parameters:

  • statement (RDF::Statement) —

    an RDF statement matching this pattern

Returns:

  • (Enumerator) —

    an enumerator yielding matching statements

See Also:

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 121

def execute(queryable, bindings = {}, &block)
  query = {
    :subject   => subject.is_a?(Variable)   && bindings[subject.to_sym]   ? bindings[subject.to_sym]   : subject,
    :predicate => predicate.is_a?(Variable) && bindings[predicate.to_sym] ? bindings[predicate.to_sym] : predicate,
    :object    => object.is_a?(Variable)    && bindings[object.to_sym]    ? bindings[object.to_sym]    : object,
    :context   => context.is_a?(Variable)   && bindings[context.to_sym]   ? bindings[context.to_sym]   : context,
  }.delete_if{|k,v| v.nil?}

  # Do all the variable terms refer to distinct variables?
  variables = self.variables
  if variable_count == variables.size
    # If so, we can just let the repository implementation handle
    # everything and yield matching statements directly:
    queryable.query(query, &block)

  # No, some terms actually refer to the same variable...
  else
    # Figure out which terms refer to the same variable:
    terms = variables.each_key.find do |name|
      terms = variable_terms(name)
      break terms if terms.size > 1
    end
    queryable.query(query) do |statement|
      # Only yield those matching statements where the variable
      # constraint is also satisfied:
      # FIXME: `Array#uniq` uses `#eql?` and `#hash`, not `#==`
      if matches = terms.map { |term| statement.send(term) }.uniq.size.equal?(1)
        block.call(statement)
      end
    end
  end
end

- (Boolean) has_variables? Also known as: variables?

Returns true if this pattern contains any variables.

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 75

def has_variables?
  subject.is_a?(Variable) ||
    predicate.is_a?(Variable) ||
    object.is_a?(Variable) ||
    context.is_a?(Variable)
end

- (Boolean) optional?

Returns true if this is an optional pattern.

Examples:

Pattern.new(:s, :p, :o).optional?                     #=> false
Pattern.new(:s, :p, :o, :optional => true).optional?  #=> true

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 92

def optional?
  !!options[:optional]
end

- (RDF::Query::Solution) solution(statement)

Returns a query solution constructed by binding any variables in this pattern with the corresponding terms in the given statement.

Examples:

pattern = Pattern.new(:s, :p, :o)
solution = pattern.solution(statement)

pattern[:s] #=> statement.subject
pattern[:p] #=> statement.predicate
pattern[:o] #=> statement.object

Parameters:

Returns:

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 170

def solution(statement)
  RDF::Query::Solution.new do |solution|
    solution[subject.to_sym]   = statement.subject   if subject.is_a?(Variable)
    solution[predicate.to_sym] = statement.predicate if predicate.is_a?(Variable)
    solution[object.to_sym]    = statement.object    if object.is_a?(Variable)
    solution[context.to_sym]   = statement.context   if context.is_a?(Variable)
  end
end

- (String) to_s

Returns a string representation of this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 296

def to_s
  StringIO.open do |buffer| # FIXME in RDF::Statement
    buffer << 'OPTIONAL ' if optional?
    buffer << [subject, predicate, object].map do |r|
      r.is_a?(RDF::Query::Variable) ? r.to_s : RDF::NTriples.serialize(r)
    end.join(" ")
    buffer << case context
      when nil, false then " ."
      when Variable then " #{context.to_s} ."
      else " #{RDF::NTriples.serialize(context)} ."
    end
    buffer.string
  end
end

- (Array) to_sxp_bin

Transform Query Pattern into an SXP

Returns:

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/sparql-da60321cd7bc/lib/sparql/algebra/extensions.rb', line 175

def to_sxp_bin
  [:triple, subject, predicate, object]
end

- (Boolean) unbound?

Returns true if all variables in this pattern are unbound.

Returns:

  • (Boolean) —

    true or false



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 280

def unbound?
  !variables.empty? && variables.values.all?(&:unbound?)
end

- (Hash{Symbol => Variable}) unbound_variables

Returns all unbound variables in this pattern.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 288

def unbound_variables
  variables.reject { |name, variable| variable.bound? }
end

- (Integer) variable_count Also known as: cardinality, arity

Returns the number of variables in this pattern.

Note: this does not count distinct variables, and will therefore e.g. return 3 even if two terms are actually the same variable.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 205

def variable_count
  count = 0
  count += 1 if subject.is_a?(Variable)
  count += 1 if predicate.is_a?(Variable)
  count += 1 if object.is_a?(Variable)
  count += 1 if context.is_a?(Variable)
  count
end

- (Array<Symbol>) variable_terms(name = nil)

Returns the variable terms in this pattern.

Examples:

Pattern.new(RDF::Node.new, :p, 123).variable_terms    #=> [:predicate]

Parameters:

  • name (Symbol, #to_sym) (defaults to: nil) —

    an optional variable name

Returns:

Since:

  • 0.3.0



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 189

def variable_terms(name = nil)
  terms = []
  terms << :subject   if subject.is_a?(Variable)   && (!name || name.eql?(subject.name))
  terms << :predicate if predicate.is_a?(Variable) && (!name || name.eql?(predicate.name))
  terms << :object    if object.is_a?(Variable)    && (!name || name.eql?(object.name))
  terms << :context   if context.is_a?(Variable)   && (!name || name.eql?(context.name))
  terms
end

- (Hash{Symbol => Variable}) variables

Returns all variables in this pattern.

Note: this returns a hash containing distinct variables only.

Returns:



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# File 'vendor/bundler/ruby/2.0.0/bundler/gems/rdf-fa5fd9674f9a/lib/rdf/query/pattern.rb', line 222

def variables
  variables = {}
  variables.merge!(subject.variables)   if subject.is_a?(Variable)
  variables.merge!(predicate.variables) if predicate.is_a?(Variable)
  variables.merge!(object.variables)    if object.is_a?(Variable)
  variables.merge!(context.variables)   if context.is_a?(Variable)
  variables
end