class RDF::Query::Pattern

An RDF query pattern.

Attributes

cost[RW]

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

@return [Numeric]

options[R]

Any additional options for this pattern.

@return [Hash]

Public Class Methods

from(pattern, graph_name: nil, **options) click to toggle source

@private @since 0.2.2

# File lib/rdf/query/pattern.rb, line 8
def self.from(pattern, graph_name: nil, **options)
  case pattern
    when Pattern then pattern
    when Array, Statement
      graph_name ||= pattern[3]
      self.new(pattern[0], pattern[1], pattern[2], graph_name: graph_name, **options)
    when Hash    then self.new(options.merge(pattern))
    else raise ArgumentError, "expected RDF::Query::Pattern, RDF::Statement, Hash, or Array, but got #{pattern.inspect}"
  end
end
new(subject = nil, predicate = nil, object = nil, options = {}) click to toggle source

@overload initialize(options = {})

@param  [Hash{Symbol => Object}]     options
@option options [Variable, Resource, Symbol, nil] :subject   (nil)
@option options [Variable, URI, Symbol, nil]      :predicate (nil)
@option options [Variable, Term, Symbol, nil]     :object    (nil)
@option options [Variable, Resource, Symbol, nil, false] :graph_name   (nil)
  A graph_name of nil matches any graph, a graph_name of false, matches only the default graph. (See {RDF::Query#initialize})
@option options [Boolean]            :optional  (false)

@overload initialize(subject, predicate, object, options = {})

@param  [Variable, Resource, Symbol, nil]         subject
@param  [Variable, URI, Symbol, nil]              predicate
@param  [Variable, Termm, Symbol, nil]            object
@param  [Hash{Symbol => Object}]          options
@option options [Variable, Resource, Symbol, nil, false] :graph_name   (nil)
  A graph_name of nil matches any graph, a graph_name of false, matches only the default graph. (See {RDF::Query#initialize})
@option options [Boolean]                 :optional  (false)

@note {Statement} treats symbols as interned {Node} instances, in a {Pattern}, they are treated as {Variable}.

Calls superclass method RDF::Statement::new
# File lib/rdf/query/pattern.rb, line 39
def initialize(subject = nil, predicate = nil, object = nil, options = {})
  super
end

Public Instance Methods

arity()
Alias for: variable_count
bind(solution) click to toggle source

Binds the pattern to a solution, making it no longer variable if all variables are resolved to bound variables

@param [RDF::Query::Solution] solution @return [self]

# File lib/rdf/query/pattern.rb, line 298
def bind(solution)
  self.to_quad.each_with_index do |term, index|
    if term.is_a?(Variable) && solution[term]
      self[index] = solution[term] 
    elsif term.is_a?(Pattern)
      term.bind(solution)
    end
  end
  self
end
binding_count() click to toggle source

Returns the number of bindings in this pattern.

@return [Integer] (0..3)

# File lib/rdf/query/pattern.rb, line 321
def binding_count
  bindings.size
end
bindings() click to toggle source

Returns all bindings in this pattern.

@return [Hash{Symbol => RDF::Term}]

# File lib/rdf/query/pattern.rb, line 329
def bindings
  bindings = {}
  bindings.merge!(subject.bindings)    if subject && subject.variable?
  bindings.merge!(predicate.bindings)  if predicate && predicate.variable?
  bindings.merge!(object.bindings)     if object && object.variable?
  bindings.merge!(graph_name.bindings) if graph_name && graph_name.variable?
  bindings
end
bindings?() click to toggle source

Returns ‘true` if this pattern contains bindings.

@return [Boolean] ‘true` or `false`

# File lib/rdf/query/pattern.rb, line 313
def bindings?
  !bindings.empty?
end
blank?() click to toggle source

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

@return [Boolean] ‘true` or `false` @since 0.3.0

# File lib/rdf/query/pattern.rb, line 85
def blank?
  subject.nil? && predicate.nil? && object.nil? && graph_name.nil?
end
bound?() click to toggle source

Returns ‘true` if all variables in this pattern are bound.

@return [Boolean] ‘true` or `false`

# File lib/rdf/query/pattern.rb, line 342
def bound?
  !variables.empty? && variables.values.all?(&:bound?)
end
bound_variables() click to toggle source

Returns all bound variables in this pattern.

@return [Hash{Symbol => Variable}]

# File lib/rdf/query/pattern.rb, line 350
def bound_variables
  variables.reject { |name, variable| variable.unbound? }
end
cardinality()
Alias for: variable_count
dup() click to toggle source

Create a new pattern from the quads, recursivly dupping sub-patterns.

# File lib/rdf/query/pattern.rb, line 64
def dup
  self.class.from(self.to_quad.map {|t| t.is_a?(RDF::Query::Pattern) ? t.dup : t})
end
eql?(other) click to toggle source

Checks pattern equality against a statement, considering nesting.

  • A pattern which has a pattern as a subject or an object, matches a statement having a statement as a subject or an object using {#eql?}.

@param [Statement] other @return [Boolean]

@see RDF::URI#== @see RDF::Node#== @see RDF::Literal#== @see RDF::Query::Variable#==

# File lib/rdf/query/pattern.rb, line 141
def eql?(other)
  return false unless other.is_a?(Statement) && (self.graph_name || false) == (other.graph_name || false)

  predicate == other.predicate &&
  (subject.is_a?(Pattern) ? subject.eql?(other.subject) : subject == other.subject) &&
  (object.is_a?(Pattern) ? object.eql?(other.object) : object == other.object)
end
execute(queryable, bindings = {}) { |statement| ... } click to toggle source

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 graph, set graph_name to ‘false`.

@example

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

@param [RDF::Queryable] queryable

the graph or repository to query

@param [Hash{Symbol => RDF::Term}, RDF::Query::Solution] bindings

optional variable bindings to use

@yield [statement]

each matching statement

@yieldparam [RDF::Statement] statement

an RDF statement matching this pattern

@return [Enumerable<RDF::Query::Pattern>]

an enumerator yielding matching statements

@see RDF::Queryable#query @since 0.3.0

# File lib/rdf/query/pattern.rb, line 173
def execute(queryable, bindings = {}, &block)
  bindings = bindings.to_h if bindings.is_a?(Solution)
  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,
    graph_name: graph_name.is_a?(Variable)  && bindings[graph_name.to_sym]  ? bindings[graph_name.to_sym] : graph_name,
  }.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
    # Considering embedding, figure out if variables that may appear more than once resolve to the same value.
    vars = variables.keys
    queryable.query(query).select do |statement|
      if vars.all? {|var| self.var_values(var, statement).uniq.size == 1}
        yield statement if block_given?
        true
      end
    end
  end
end
has_variables?()
Alias for: variables?
initialize!() click to toggle source

@private

Calls superclass method RDF::Statement#initialize!
# File lib/rdf/query/pattern.rb, line 45
def initialize!
  @graph_name = Variable.new(@graph_name) if @graph_name.is_a?(Symbol)
  @subject    = Variable.new(@subject)    if @subject.is_a?(Symbol)
  @predicate  = Variable.new(@predicate)  if @predicate.is_a?(Symbol)
  @object     = Variable.new(@object)     if @object.is_a?(Symbol)

  # Estmate cost positionally, with variables being least expensive as objects, then predicates, then subjects, then graph_names.
  # XXX does not consider bound variables, which would need to be dynamically calculated.
  @cost = (@object.nil?     || @object.is_a?(Variable)      ? 8 : 0) +
          (@predicate.nil?  || @predicate.is_a?(Variable)   ? 4 : 0) +
          (@subject.nil?    || @subject.is_a?(Variable)     ? 2 : 0) +
          (@graph_name.is_a?(Variable)                      ? 1 : 0) +
          (@object.is_a?(Pattern)                           ? (@object.cost * 4) : 0) +
          (@subject.is_a?(Pattern)                          ? (@subject.cost * 2) : 0)
  super
end
optional?() click to toggle source

Returns ‘true` if this is an optional pattern.

@example

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

@return [Boolean] ‘true` or `false` @since 0.3.0

# File lib/rdf/query/pattern.rb, line 111
def optional?
  !!options[:optional]
end
solution(statement) click to toggle source

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

@example

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

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

@param [RDF::Statement] statement

an RDF statement to bind terms from

@return [RDF::Query::Solution] @since 0.3.0

# File lib/rdf/query/pattern.rb, line 218
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[graph_name.to_sym] = statement.graph_name if graph_name.is_a?(Variable)
    solution.merge!(subject.solution(statement.subject)) if subject.respond_to?(:solution)
    solution.merge!(object.solution(statement.object)) if object.respond_to?(:solution)
  end
end
to_s() click to toggle source

Returns a string representation of this pattern.

@return [String]

Calls superclass method RDF::Statement#to_s
# File lib/rdf/query/pattern.rb, line 374
def to_s
  (optional? ? 'OPTIONAL ' : '') + super
end
unbound?() click to toggle source

Returns ‘true` if all variables in this pattern are unbound.

@return [Boolean] ‘true` or `false`

# File lib/rdf/query/pattern.rb, line 358
def unbound?
  !variables.empty? && variables.values.all?(&:unbound?)
end
unbound_variables() click to toggle source

Returns all unbound variables in this pattern.

@return [Hash{Symbol => Variable}]

# File lib/rdf/query/pattern.rb, line 366
def unbound_variables
  variables.reject { |name, variable| variable.bound? }
end
valid?() click to toggle source

Is this pattern composed only of valid components?

@return [Boolean] ‘true` or `false`

# File lib/rdf/query/pattern.rb, line 119
def valid?
  (subject?   ? (subject.resource? || subject.variable?) && subject.valid? : true) && 
  (predicate? ? (predicate.uri? || predicate.variable?) && predicate.valid? : true) &&
  (object?    ? (object.term? || object.variable?) && object.valid? : true) &&
  (graph?     ? (graph_name.resource? || graph_name.variable?) && graph_name.valid? : true)
rescue NoMethodError
  false
end
var_values(var, statement) click to toggle source

Returns all values the statement in the same pattern position

@param [Symbol] var @param [RDF::Statement] statement @return [Array<RDF::Term>]

# File lib/rdf/query/pattern.rb, line 257
def var_values(var, statement)
  %i(subject predicate object graph_name).map do |position|
    po = self.send(position)
    so = statement.send(position)
    po.var_values(var, so) if po.respond_to?(:var_values)
  end.flatten.compact
end
variable_count() click to toggle source

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.

@return [Integer] (0..3)

# File lib/rdf/query/pattern.rb, line 272
def variable_count
  [subject, predicate, object, graph_name].inject(0) do |memo, term|
    memo += (term.is_a?(Variable) ? 1 :
             (term.respond_to?(:variable_count) ? term.variable_count : 0))
  end
end
Also aliased as: cardinality, arity
variable_terms(name = nil) click to toggle source

Returns the variable terms in this pattern.

@example

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

@param [Symbol, to_sym] name

an optional variable name

@return [Array<Symbol>] @deprecated use {#var_values} instead @since 0.3.0

# File lib/rdf/query/pattern.rb, line 240
def variable_terms(name = nil)
  warn "[DEPRECATION] RDF::Query::Pattern#variable_terms is deprecated and will be removed in a future version.\n" +
       "Called from #{Gem.location_of_caller.join(':')}"
  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 << :graph_name if graph_name.is_a?(Variable) && (!name || name.eql?(graph_name.name))
  terms
end
variables() click to toggle source

Returns all variables in this pattern.

Note: this returns a hash containing distinct variables only.

@return [Hash{Symbol => Variable}]

# File lib/rdf/query/pattern.rb, line 287
def variables
  [subject, predicate, object, graph_name].inject({}) do |memo, term|
    term && term.variable? ? memo.merge(term.variables) : memo
  end
end
variables?() click to toggle source

Returns ‘true` if this pattern contains any variables.

@return [Boolean] ‘true` or `false` @since 0.3.0

# File lib/rdf/query/pattern.rb, line 94
def variables?
  subject    && subject.variable? ||
  predicate  && predicate.variable? ||
  object     && object.variable? ||
  graph_name && graph_name.variable?
end
Also aliased as: has_variables?