Class: RDF::N3::Algebra::Formula

Inherits:
SPARQL::Algebra::Operator show all
Includes:
Enumerable, Builtin, Term, SPARQL::Algebra::Query, SPARQL::Algebra::Update
Defined in:
lib/rdf/n3/algebra/formula.rb

Overview

A Notation3 Formula combines a graph with a BGP query.

Constant Summary collapse

NAME = 
:formula

Instance Attribute Summary collapse

Attributes included from Enumerable

#existentials, #universals

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Builtin

#input_operand, #rank

Methods included from Term

#as_datetime, #as_number, #sameTerm?

Methods inherited from SPARQL::Algebra::Operator

#formulae, #operands=

Instance Attribute Details

#query ⇒ RDF::Query

Query to run against a queryable to determine if the formula matches the queryable.

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 17

def query
  @query
end

Class Method Details

.from_enumerable(enumerable, **options) ⇒ RDF::N3::Algebra::Formula

Create a formula from an RDF::Enumerable (such as RDF::N3::Repository)

Parameters:

  • enumerable (RDF::Enumerable)
  • options (Hash{Symbol => Object}) —

    any additional keyword options

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 28

def self.from_enumerable(enumerable, **options)
  # SPARQL used for SSE and algebra functionality
  require 'sparql' unless defined?(:SPARQL)

  # Create formulae from statement graph_names
  formulae = {}
  enumerable.graph_names.unshift(nil).each do |graph_name|
    formulae[graph_name] = Formula.new(graph_name: graph_name, formulae: formulae, **options)
  end

  # Add patterns to appropiate formula based on graph_name,
  # and replace subject and object bnodes which identify
  # named graphs with those formula
  enumerable.each_statement do |statement|
    # A graph name indicates a formula.
    graph_name = statement.graph_name
    form = formulae[graph_name]

    # Map statement components to formulae, if necessary.
    statement = RDF::Statement.from(statement.to_a.map do |term|
      case term
      when RDF::Node
        term = if formulae[term]
          # Transform blank nodes denoting formulae into those formulae
          formulae[term]
        elsif graph_name
          # If we're in a quoted graph, transform blank nodes into undistinguished existential variables.
          term.to_ndvar(graph_name)
        else
          term
        end
      when RDF::N3::List
        # Transform blank nodes denoting formulae into those formulae
        term = term.transform {|t| t.node? ? formulae.fetch(t, t) : t}

        # If we're in a quoted graph, transform blank node components into existential variables
        if graph_name && term.has_nodes?
          term = term.to_ndvar(graph_name)
        end
      end
      term
    end)

    pattern = statement.variable? ? RDF::Query::Pattern.from(statement) : statement

    # Formulae may be the subject or object of a known operator
    if klass = RDF::N3::Algebra.for(pattern.predicate)
      form.operands << klass.new(pattern.subject,
                                 pattern.object,
                                 formulae: formulae,
                                 parent: form,
                                 predicate: pattern.predicate,
                                 **options)
    else
      pattern.graph_name = nil
      form.operands << pattern
    end
  end

  # Formula is that without a graph name
  this = formulae[nil]

  # If assigned a graph name, add it here
  this.graph_name = options[:graph_name] if options[:graph_name]
  this
end

Instance Method Details

#deep_dup ⇒ RDF::N3::Algebra::Formula

Duplicate this formula, recursively, renaming graph names using hash function.

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 99

def deep_dup
  #new_ops = operands.map(&:dup)
  new_ops = operands.map do |op|
    op.deep_dup
  end
  graph_name = RDF::Node.intern(new_ops.hash)
  log_debug("formula") {"dup: #{self.graph_name} to #{graph_name}"}
  self.class.new(*new_ops, **@options.merge(graph_name: graph_name, formulae: formulae))
end

#distinguished_vars ⇒ Array<RDF::Query::Variable]

Distinguished vars in this formula

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 402

def distinguished_vars
  @distinguished ||= vars.vars.select(&:distinguished?)
end

#each(solutions: RDF::Query::Solutions(RDF::Query::Solution.new)) {|statement| ... } ⇒ Object

Yields each statement from this formula bound to previously determined solutions.

Yields:

  • (statement) —

    each matching statement

Yield Parameters:

Yield Returns:

  • (void) —

    ignored



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# File 'lib/rdf/n3/algebra/formula.rb', line 236

def each(solutions: RDF::Query::Solutions(RDF::Query::Solution.new), &block)
  log_debug("(formula each)") {SXP::Generator.string([self, solutions].to_sxp_bin)}

  # Yield statements by binding variables
  solutions.each do |solution|
    # Bind blank nodes to the solution when it doesn't contain a solution for an existential variable
    existential_vars.each do |var|
      solution[var.name] ||= RDF::Node.intern(var.name.to_s.sub(/^\$+/, ''))
    end

    log_debug("(formula apply)") {solution.to_sxp}
    # Yield each variable statement which is constant after applying solution
    log_depth do
      n3statements.each do |statement|
        terms = {}
        [:subject, :predicate, :object].each do |part|
          terms[part] = case o = statement.send(part)
          when RDF::Query::Variable
            if solution[o] && solution[o].formula?
              log_info("(formula from var form)") {solution[o].graph_name.to_sxp}
              form_statements(solution[o], solution: solution, &block)
            else
              solution[o] || o
            end
          when RDF::N3::List
            o.variable? ? o.evaluate(solution.bindings, formulae: formulae) : o
          when RDF::N3::Algebra::Formula
            # uses the graph_name of the formula, and yields statements from the formula. No solutions are passed in.
            log_info("(formula from form)") {o.graph_name.to_sxp}
            form_statements(o, solution: solution, &block)
          else
            o
          end
        end

        statement = RDF::Statement.from(terms)
        log_debug("(formula add)") {statement.to_sxp}

        block.call(statement)
      end

      # statements from sub-operands
      sub_ops.each do |op|
        log_debug("(formula sub_op)") {SXP::Generator.string [op, solution].to_sxp_bin}
        op.each(solutions: RDF::Query::Solutions(solution)) do |stmt|
          log_debug("(formula add from sub_op)") {stmt.to_sxp}
          block.call(stmt)
          # Add statements for any term which is a formula
          stmt.to_a.select(&:node?).map {|n| formulae[n]}.compact.each do |ef|
            log_debug("(formula from form)") {ef.graph_name.to_sxp}
            form_statements(ef, solution: solution, &block)              
          end
        end
      end
    end
  end
end

#each_pattern {|pattern| ... } ⇒ Object

Yields each pattern which is not a builtin

Yields:

  • (pattern) —

    each matching pattern

Yield Parameters:

Yield Returns:

  • (void) —

    ignored



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# File 'lib/rdf/n3/algebra/formula.rb', line 301

def each_pattern(&block)
  n3statements.each do |statement|
    terms = {}
    [:subject, :predicate, :object].each do |part|
      terms[part] = case o = statement.send(part)
      when RDF::N3::Algebra::Formula
        form_statements(o, solution: RDF::Query::Solution.new(), &block)
      else
        o
      end
    end

    pattern = RDF::Query::Pattern.from(terms)
    block.call(pattern)
  end
end

#evaluate(bindings, formulae:, **options) ⇒ RDF::N3::List

Evaluates the formula using the given variable bindings by cloning the formula replacing variables with their bindings recursively.

Parameters:

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

    a query solution containing zero or more variable bindings

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

    ({}) options passed from query

Returns:

See Also:

  • SPARQL::Algebra::Expression.evaluate


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# File 'lib/rdf/n3/algebra/formula.rb', line 200

def evaluate(bindings, formulae:, **options)
  return self if bindings.empty?
  this = dup
  # Maintain formula relationships
  formulae {|k, v| this.formulae[k] ||= v}

  # Replace operands with bound operands
  this.operands = operands.map do |op|
    op.evaluate(bindings, formulae: formulae, **options)
  end
  this
end

#execute(queryable, solutions: RDF::Query::Solutions(RDF::Query::Solution.new), **options) ⇒ RDF::Solutions

Yields solutions from patterns and other operands. Solutions are created by evaluating each pattern and other sub-operand against queryable.

When executing, blank nodes are turned into non-distinguished existential variables, noted with $$. These variables are removed from the returned solutions, as they can’t be bound outside of the formula.

Parameters:

  • queryable (RDF::Queryable) —

    the graph or repository to query

  • solutions (RDF::Query::Solutions) (defaults to: RDF::Query::Solutions(RDF::Query::Solution.new)) —

    initial solutions for chained queries (RDF::Query::Solutions(RDF::Query::Solution.new))

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

    any additional keyword options

Returns:

  • (RDF::Solutions) —

    distinct solutions



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# File 'lib/rdf/n3/algebra/formula.rb', line 121

def execute(queryable, solutions: RDF::Query::Solutions(RDF::Query::Solution.new), **options)
  log_info("formula #{graph_name}") {SXP::Generator.string operands.to_sxp_bin}
  log_debug("(formula bindings)") { SXP::Generator.string solutions.to_sxp_bin}

  @query ||= RDF::Query.new(patterns).optimize!
  log_info("(formula query)") { SXP::Generator.string(@query.to_sxp_bin)}

  solutions = if @query.empty?
    solutions
  else
    these_solutions = queryable.query(@query, solutions: solutions, **options)
    if these_solutions.empty?
      # Pattern doesn't match, so there can be no solutions
      log_debug("(formula query solutions)") { SXP::Generator.string([].to_sxp_bin)}
      RDF::Query::Solutions.new
    else
      these_solutions.map! do |solution|
        RDF::Query::Solution.new(solution.to_h.inject({}) do |memo, (name, value)|
          # Replace blank node bindings with lists and formula references with formula, where those blank nodes are associated with lists.
          value = formulae.fetch(value, value) if value.node?
          l = RDF::N3::List.try_list(value, queryable)
          value = l if l.constant?
          memo.merge(name => value)
        end)
      end
      log_debug("(formula query solutions)") { SXP::Generator.string(these_solutions.to_sxp_bin)}
      solutions.merge(these_solutions)
    end
  end

  return solutions if solutions.empty?

  # Reject solutions which include variables as values
  solutions.filter! {|s| s.enum_value.none?(&:variable?)}

  # Use our solutions for sub-ops
  # Join solutions from other operands
  #
  # * Order operands by those having inputs which are constant or bound.
  # * Run built-ins with indeterminant inputs (two-way) until any produces non-empty solutions, and then run remaining built-ins until exhasted or finished.
  # * Re-calculate inputs with bound inputs after each built-in is run.
  log_depth do
    # Iterate over sub_ops using evaluation heuristic
    ops = sub_ops.sort_by {|op| op.rank(solutions)}
    while !ops.empty?
      last_op = nil
      ops.each do |op|
        log_debug("(formula built-in)") {SXP::Generator.string op.to_sxp_bin}
        these_solutions = op.execute(queryable, solutions: solutions)
        # If there are no solutions, try the next one, until we either run out of operations, or we have solutions
        next if these_solutions.empty?
        last_op = op
        solutions = RDF::Query::Solutions(these_solutions)
        break
      end

      # If there is no last_op, there are no solutions.
      unless last_op
        solutions = RDF::Query::Solutions.new
        break
      end

      # Remove op from list, and re-order remaining ops.
      ops = (ops - [last_op]).sort_by {|op| op.rank(solutions)}
    end
  end
  log_info("(formula sub-op solutions)") {SXP::Generator.string solutions.to_sxp_bin}
  solutions
end

#existential_vars ⇒ Array<RDF::Query::Variable]

Existential vars in this formula

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 395

def existential_vars
  @existentials ||= vars.select(&:existential?)
end

#formula? ⇒ Boolean

Returns true if self is a RDF::N3::Algebra::Formula.

Returns:

  • (Boolean) 


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# File 'lib/rdf/n3/algebra/formula.rb', line 217

def formula?
  true
end

#graph_name ⇒ RDF::Resource Also known as: to_uri

Graph name associated with this formula

Returns:

  • (RDF::Resource) 


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# File 'lib/rdf/n3/algebra/formula.rb', line 320

def graph_name; @options[:graph_name]; end

#graph_name=(name) ⇒ RDF::Resource

Assign a graph name to this formula

Parameters:

  • name (RDF::Resource)

Returns:

  • (RDF::Resource) 


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# File 'lib/rdf/n3/algebra/formula.rb', line 330

def graph_name=(name)
  formulae[name] = self
  @options[:graph_name] = name
end

#hash ⇒ Object

The formula hash is the hash of it’s operands and graph_name.

See Also:

  • Value#hash


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# File 'lib/rdf/n3/algebra/formula.rb', line 225

def hash
  ([graph_name] + operands).hash
end

#inspect ⇒ Object 



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# File 'lib/rdf/n3/algebra/formula.rb', line 426

def inspect
  sprintf("#<%s:%s(%d)>", self.class.name, self.graph_name, self.operands.count)
end

#n3statements ⇒ Object

Statements memoizer, from the operands which are statements.

Statements may include embedded formulae.



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# File 'lib/rdf/n3/algebra/formula.rb', line 339

def n3statements
  # BNodes in statements are existential variables.
  @n3statements ||= begin
    # Operations/Builtins are not statements.
    operands.
      select {|op| op.is_a?(RDF::Statement)}
  end
end

#patterns ⇒ Object

Patterns memoizer, from the operands which are statements and not builtins.

Expands statements containing formulae into their statements.



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# File 'lib/rdf/n3/algebra/formula.rb', line 352

def patterns
  # BNodes in statements are existential variables.
  @patterns ||= enum_for(:each_pattern).to_a
end

#sub_ops ⇒ Object

Non-statement operands memoizer



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# File 'lib/rdf/n3/algebra/formula.rb', line 359

def sub_ops
  # operands that aren't statements, ordered by their graph_name
  @sub_ops ||= operands.reject {|op| op.is_a?(RDF::Statement)}.map do |op|
    # Substitute nodes for existential variables in operator operands
    op.operands.map! do |o|
      case o
      when RDF::N3::List
        # Substitute blank node members with existential variables, recusively.
        graph_name && o.has_nodes? ? o.to_ndvar(graph_name) : o
      when RDF::Node
        graph_name ? o.to_ndvar(graph_name) : o
      else
        o
      end
    end
    op
  end
end

#to_base ⇒ Object 



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# File 'lib/rdf/n3/algebra/formula.rb', line 422

def to_base
  inspect
end

#to_s ⇒ Object 



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# File 'lib/rdf/n3/algebra/formula.rb', line 413

def to_s
  to_sxp
end

#to_sxp_bin ⇒ Object 



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# File 'lib/rdf/n3/algebra/formula.rb', line 417

def to_sxp_bin
  [:formula, graph_name].compact +
  operands.map(&:to_sxp_bin)
end

#undistinguished_vars ⇒ Array<RDF::Query::Variable]

Undistinguished vars in this formula

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 409

def undistinguished_vars
  @undistinguished ||= vars.vars.reject(&:distinguished?)
end

#universal_vars ⇒ Array<RDF::Query::Variable]

Universal vars in this formula and sub-formulae

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 388

def universal_vars
  @universals ||= vars.reject(&:existential?).uniq
end

#vars ⇒ Array<RDF::Query::Variable>

Return the variables contained within this formula

Returns:



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# File 'lib/rdf/n3/algebra/formula.rb', line 381

def vars
  operands.vars.flatten.compact
end