Class: RDF::Query::Pattern

Inherits:
Statement show all
Defined in:
lib/rdf/query/pattern.rb

Overview

An RDF query pattern.

Since:

  • 0.3.0

Instance Attribute Summary collapse

Attributes inherited from Statement

#graph_name, #id, #object, #predicate, #subject

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Statement

#==, #===, #[], #[]=, #asserted?, #canonicalize, #canonicalize!, #complete?, #embedded?, #has_graph?, #has_object?, #has_predicate?, #has_subject?, #hash, #incomplete?, #inferred?, #invalid?, #node?, #quoted?, #reified, #statement?, #to_h, #to_quad, #to_triple, #variable?

Methods included from Resource

new, #resource?

Methods included from Term

#<=>, #==, #compatible?, #term?, #to_base, #to_term

Methods included from Value

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

Constructor Details

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

Note:

Statement treats symbols as interned Node instances, in a RDF::Query::Pattern, they are treated as Variable.

Returns a new instance of Pattern.

Overloads:

  • #initialize(options = {}) ⇒ Pattern

    Parameters:

    • options (Hash{Symbol => Object}) (defaults to: {})

    Options Hash (options):

    • :subject (Variable, Resource, Symbol, nil) — default: nil
    • :predicate (Variable, URI, Symbol, nil) — default: nil
    • :object (Variable, Term, Symbol, nil) — default: nil
    • :graph_name (Variable, Resource, Symbol, nil, false) — default: nil —

      A graph_name of nil matches any graph, a graph_name of false, matches only the default graph.

    • :optional (Boolean) — default: false
  • #initialize(subject, predicate, object, options = {}) ⇒ Pattern

    Parameters:

    Options Hash (options):

    • :graph_name (Variable, Resource, Symbol, nil, false) — default: nil —

      A graph_name of nil matches any graph, a graph_name of false, matches only the default graph.

    • :optional (Boolean) — default: false

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 39

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

Instance Attribute Details

#cost ⇒ Numeric

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

Returns:

  • (Numeric)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 72

def cost
  @cost
end

#options ⇒ Hash (readonly)

Any additional options for this pattern.

Returns:

  • (Hash)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 66

def options
  @options
end

Class Method Details

.from(pattern, graph_name: nil, **options) ⇒ Object

Since:

  • 0.2.2



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# 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

Instance Method Details

#bind(solution) ⇒ self

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

Parameters:

Returns:

  • (self)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 280

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 ⇒ Integer

Returns the number of bindings in this pattern.

Returns:

  • (Integer) —

    (0..3)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 303

def binding_count
  bindings.size
end

#bindings ⇒ Hash{Symbol => RDF::Term}

Returns all bindings in this pattern.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 311

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

#bindings? ⇒ Boolean

Returns true if this pattern contains bindings.

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 295

def bindings?
  !bindings.empty?
end

#blank? ⇒ Boolean

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 'lib/rdf/query/pattern.rb', line 79

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

#bound? ⇒ Boolean

Returns true if all variables in this pattern are bound.

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 324

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

#bound_variables ⇒ Hash{Symbol => Variable}

Returns all bound variables in this pattern.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 332

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

#eql?(other) ⇒ Boolean

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?.

Parameters:

Returns:

  • (Boolean)

See Also:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 135

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| ... } ⇒ Enumerable<RDF::Query::Pattern>

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.

Examples:

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

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • bindings (Hash{Symbol => RDF::Term}) (defaults to: {}) —

    optional variable bindings to use

Yields:

  • (statement) —

    each matching statement

Yield Parameters:

  • statement (RDF::Statement) —

    an RDF statement matching this pattern

Returns:

See Also:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 167

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,
    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
    # 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).select do |statement|
      # Only yield those matching statements where the variable
      # constraint is also satisfied:
      # FIXME: `Array#uniq` uses `#eql?` and `#hash`, not `#==`
      if terms.map { |term| statement.send(term) }.uniq.size.equal?(1)
        yield statement if block_given?
        true
      end
    end
  end
end

#has_variables? ⇒ Boolean 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 'lib/rdf/query/pattern.rb', line 88

def has_variables?
  subject    && subject.variable? ||
  predicate  && predicate.variable? ||
  object     && object.variable? ||
  graph_name && graph_name.variable?
end

#initialize! ⇒ Object

Since:

  • 0.3.0



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# 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? ⇒ Boolean

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 'lib/rdf/query/pattern.rb', line 105

def optional?
  !!options[:optional]
end

#solution(statement) ⇒ RDF::Query::Solution

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 'lib/rdf/query/pattern.rb', line 217

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.is_a?(Pattern)
    solution.merge!(object.solution(statement.object)) if object.is_a?(Pattern)
  end
end

#to_s ⇒ String

Returns a string representation of this pattern.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 356

def to_s
  StringIO.open do |buffer| # FIXME in RDF::Statement
    buffer << 'OPTIONAL ' if optional?
    buffer << [subject, predicate, object].map do |r|
      if r.is_a?(RDF::Query::Variable)
        r.to_s
      elsif r.is_a?(RDF::Query::Pattern)
        "<<#{r.to_s[0..-3]}>>"
      else
        RDF::NTriples.serialize(r)
      end
    end.join(" ")
    buffer << case graph_name
      when nil, false then " ."
      when Variable then " #{graph_name.to_s} ."
      else " #{RDF::NTriples.serialize(graph_name)} ."
    end
    buffer.string
  end
end

#unbound? ⇒ Boolean

Returns true if all variables in this pattern are unbound.

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 340

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

#unbound_variables ⇒ Hash{Symbol => Variable}

Returns all unbound variables in this pattern.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 348

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

#valid? ⇒ Boolean

Is this pattern composed only of valid components?

Returns:

  • (Boolean) —

    true or false

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 113

def valid?
  (has_subject?   ? (subject.resource? || subject.variable?) && subject.valid? : true) && 
  (has_predicate? ? (predicate.uri? || predicate.variable?) && predicate.valid? : true) &&
  (has_object?    ? (object.term? || object.variable?) && object.valid? : true) &&
  (has_graph?     ? (graph_name.resource? || graph_name.variable?) && graph_name.valid? : true)
rescue NoMethodError
  false
end

#variable_count ⇒ Integer 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:

  • (Integer) —

    (0..3)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 254

def variable_count
  [subject, predicate, object, graph_name].inject(0) do |memo, term|
    memo += (term.is_a?(Variable) ? 1 :
             (term.is_a?(Pattern) ? term.variable_count : 0))
  end
end

#variable_terms(name = nil) ⇒ Array<Symbol>

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:

  • (Array<Symbol>)

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 238

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 << :graph_name if graph_name.is_a?(Variable) && (!name || name.eql?(graph_name.name))
  terms
end

#variables ⇒ Hash{Symbol => Variable}

Returns all variables in this pattern.

Note: this returns a hash containing distinct variables only.

Returns:

Since:

  • 0.3.0



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# File 'lib/rdf/query/pattern.rb', line 269

def variables
  [subject, predicate, object, graph_name].inject({}) do |memo, term|
    term && term.variable? ? memo.merge(term.variables) : memo
  end
end