Module: SPARQL::Algebra::Expression Abstract

Included in:
RDF::Query::Variable, RDF::Term, Operator
Defined in:
lib/sparql/algebra/expression.rb

Overview

This module is abstract.

A SPARQL algebra expression.

Class Method Summary collapse

Instance Method Summary collapse

Class Method Details

.cast(datatype, value) ⇒ Boolean

Casts operand as the specified datatype

Raises:

  • (TypeError) —

    if datatype is not a URI or value cannot be cast to datatype

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 136

def self.cast(datatype, value)
  case datatype
  when RDF::XSD.dateTime
    case value
    when RDF::Literal::DateTime, RDF::Literal::Date, RDF::Literal::Time
      RDF::Literal.new(value, :datatype => datatype)
    when RDF::Literal::Numeric, RDF::Literal::Boolean, RDF::URI, RDF::Node
      raise TypeError, "Value #{value.inspect} cannot be cast as #{datatype}"
    else
      RDF::Literal.new(value.value, :datatype => datatype, :validate => true)
    end
  when RDF::XSD.float, RDF::XSD.double
    case value
    when RDF::Literal::Numeric, RDF::Literal::Boolean
      RDF::Literal.new(value, :datatype => datatype)
    when RDF::Literal::DateTime, RDF::Literal::Date, RDF::Literal::Time, RDF::URI, RDF::Node
      raise TypeError, "Value #{value.inspect} cannot be cast as #{datatype}"
    else
      RDF::Literal.new(value.value, :datatype => datatype, :validate => true)
    end
  when RDF::XSD.boolean
    case value
    when RDF::Literal::Boolean
      value
    when RDF::Literal::Numeric
      RDF::Literal::Boolean.new(value.value != 0)
    when RDF::Literal::DateTime, RDF::Literal::Date, RDF::Literal::Time, RDF::URI, RDF::Node
      raise TypeError, "Value #{value.inspect} cannot be cast as #{datatype}"
    else
      RDF::Literal.new(!value.to_s.empty?, :datatype => datatype, :validate => true)
    end
  when RDF::XSD.decimal, RDF::XSD.integer
    case value
    when RDF::Literal::Integer, RDF::Literal::Decimal, RDF::Literal::Boolean
      RDF::Literal.new(value, :datatype => datatype)
    when RDF::Literal::DateTime, RDF::Literal::Date, RDF::Literal::Time, RDF::URI, RDF::Node
      raise TypeError, "Value #{value.inspect} cannot be cast as #{datatype}"
    else
      RDF::Literal.new(value.value, :datatype => datatype, :validate => true)
    end
  when RDF::XSD.string
     RDF::Literal.new(value, :datatype => datatype)
  else
    raise TypeError, "Expected datatype (#{datatype}) to be an XSD type"
  end
rescue
  raise TypeError, $!.message
end

.for(*sse) ⇒ Expression Also known as: []

Examples:

Expression.for(:isLiteral, RDF::Literal(3.1415))
Expression[:isLiteral, RDF::Literal(3.1415)]

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

def self.for(*sse)
  self.new(sse)
end

.new(sse, options = {}) ⇒ Expression

Examples:

Expression.new([:isLiteral, RDF::Literal(3.1415)], :version => 1.0)

Raises:

  • (TypeError) —

    if any of the operands is invalid


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# File 'lib/sparql/algebra/expression.rb', line 87

def self.new(sse, options = {})
  raise ArgumentError, "invalid SPARQL::Algebra::Expression form: #{sse.inspect}" unless sse.is_a?(Array)

  operator = Operator.for(sse.first, sse.length - 1)
  unless operator
    return case sse.first
    when Array
      debug("Map array elements #{sse}", options)
      sse.map {|s| self.new(s, options.merge(:depth => options[:depth].to_i + 1))}
    else
      debug("No operator found for #{sse.first}", options)
      sse.map do |s|
        s.is_a?(Array) ?
          self.new(s, options.merge(:depth => options[:depth].to_i + 1)) :
          s
      end
    end
  end

  operands = sse[1..-1].map do |operand|
    debug("Operator=#{operator.inspect}, Operand=#{operand.inspect}", options)
    case operand
      when Array
        self.new(operand, options.merge(:depth => options[:depth].to_i + 1))
      when Operator, Variable, RDF::Term, RDF::Query, Symbol
        operand
      when TrueClass, FalseClass, Numeric, String, DateTime, Date, Time
        RDF::Literal(operand)
      else raise TypeError, "invalid SPARQL::Algebra::Expression operand: #{operand.inspect}"
    end
  end

  debug("#{operator.inspect}(#{operands.map(&:inspect).join(',')})", options)
  options.delete_if {|k, v| [:debug, :depth, :prefixes, :base_uri].include?(k) }
  operands << options unless options.empty?
  operator.new(*operands)
end

.open(filename, options = {}) {|expression| ... } ⇒ Expression

Parses input from the given file name or URL.

Options Hash (options):

  • :base_uri (RDF::URI, #to_s) —

    Base URI used for loading relative URIs.

Yields:

  • (expression)

Yield Parameters:

Yield Returns:

  • (void) —

    ignored


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# File 'lib/sparql/algebra/expression.rb', line 55

def self.open(filename, options = {}, &block)
  RDF::Util::File.open_file(filename, options) do |file|
    options[:base_uri] ||= filename
    expression = Expression.parse(file, options)
    yield(expression) if block_given?
    expression
  end
end

.parse(sse, options = {}) {|expression| ... } ⇒ Expression

Examples:

Expression.parse('(isLiteral 3.1415)')

Options Hash (options):

  • :base_uri (RDF::URI, #to_s) —

    Base URI used for loading relative URIs.

Yields:

  • (expression)

Yield Parameters:

Yield Returns:

  • (void) —

    ignored


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# File 'lib/sparql/algebra/expression.rb', line 22

def self.parse(sse, options = {}, &block)
  begin
    require 'sxp' # @see http://rubygems.org/gems/sxp
  rescue LoadError
    abort "SPARQL::Algebra::Expression.parse requires the SXP gem (hint: `gem install sxp')."
  end
  require 'sparql/algebra/sxp_extensions'
  
  sxp = SXP::Reader::SPARQL.new(sse)
  sxp_result = sxp.read

  Operator.base_uri = options.delete(:base_uri) if options.has_key?(:base_uri)
  Operator.prefixes = sxp.prefixes || {}

  expression = self.new(sxp_result, options)

  yield(expression) if block_given?
  expression
end

Instance Method Details

#constant? ⇒ Boolean

Returns true.

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 199

def constant?
  !(variable?)
end

#evaluate(bindings = {}) ⇒ Expression

Evaluates this expression using the given variable bindings.

This is the default implementation, which simply returns self. Subclasses can override this method in order to implement something more useful.


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# File 'lib/sparql/algebra/expression.rb', line 224

def evaluate(bindings = {})
  self
end

#optimize ⇒ Expression

Returns an optimized version of this expression.

This is the default implementation, which simply returns self. Subclasses can override this method in order to implement something more useful.


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# File 'lib/sparql/algebra/expression.rb', line 211

def optimize
  self
end

#to_sse ⇒ Array

Returns the SPARQL S-Expression (SSE) representation of this expression.

This is the default implementation, which simply returns self. Subclasses can override this method in order to implement something more useful.

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 237

def to_sse
  self
end

#variable? ⇒ Boolean

Returns false.

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 190

def variable?
  false
end