Module: SPARQL::Algebra::Expression Abstract

Includes:
RDF::Util::Logger
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) ⇒ RDF::Term

Casts operand as the specified datatype

Parameters:

  • datatype (RDF::URI)

    Datatype to evaluate, one of: xsd:integer, xsd:decimal xsd:float, xsd:double, xsd:string, xsd:boolean, or xsd:dateTime

  • value (RDF::Term)

    Value, which should be a typed literal, where the type must be that specified

Returns:

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 217

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::Boolean
      RDF::Literal.new(value.object ? 1 : 0, datatype: datatype)
    when RDF::Literal::Numeric
      RDF::Literal.new(value.to_f, 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.object != 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::Boolean.new(value.value, datatype: datatype, validate: true)
    end
  when RDF::XSD.decimal, RDF::XSD.integer
    case value
    when RDF::Literal::Boolean
      RDF::Literal.new(value.object ? 1 : 0, datatype: datatype)
    when RDF::Literal::Numeric
      RDF::Literal.new(value.object, 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
    # Cast to string rules based on https://www.w3.org/TR/xpath-functions/#casting-to-string
    case value
    when RDF::Literal::Integer
      RDF::Literal.new(value.canonicalize.to_s, datatype: datatype)
    when RDF::Literal::Decimal
      if value == value.ceil
        RDF::Literal.new(value.ceil, datatype: datatype)
      else
        RDF::Literal.new(value.canonicalize.to_s, datatype: datatype)
      end
    when RDF::Literal::Float, RDF::Literal::Double
      if value.abs >= 0.000001 && value.abs < 1000000
        # If SV has an absolute value that is greater than or equal to 0.000001 (one millionth) and less than 1000000 (one million), then the value is converted to an xs:decimal and the resulting xs:decimal is converted to an xs:string according to the rules above, as though using an implementation of xs:decimal that imposes no limits on the totalDigits or fractionDigits facets.
        cast(datatype, RDF::Literal::Decimal.new(value.object))
      elsif value.object.zero?
        # If SV has the value positive or negative zero, TV is "0" or "-0" respectively.
        RDF::Literal.new(value.to_s.start_with?('-') ? '-0' : '0', datatype: datatype)
      else
        # If SV is positive or negative infinity, TV is the string "INF" or "-INF" respectively.
        # In other cases, the result consists of a mantissa, which has the lexical form of an xs:decimal, followed by the letter "E", followed by an exponent which has the lexical form of an xs:integer. Leading zeroes and "+" signs are prohibited in the exponent. For the mantissa, there must be a decimal point, and there must be exactly one digit before the decimal point, which must be non-zero. The "+" sign is prohibited. There must be at least one digit after the decimal point. Apart from this mandatory digit, trailing zero digits are prohibited.
        RDF::Literal.new(value.canonicalize.to_s, datatype: datatype)
      end
    else
      RDF::Literal.new(value.canonicalize.to_s, datatype: datatype)
    end
  else
    raise TypeError, "Expected datatype (#{datatype}) to be a recognized XPath function"
  end
rescue
  raise TypeError, $!.message
end

.extension(function, *args) ⇒ RDF::Term

Invoke an extension function.

Applies a registered extension function, if registered. Otherwise, if it is an XSD Constructor function, apply that.

Parameters:

  • function (RDF::URI)
  • args (Array<RDF::Term>)

    splat of args to function

Returns:

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 196

def self.extension(function, *args)
  if function.to_s.start_with?(RDF::XSD.to_s)
    self.cast(function, args.first)
  elsif extension_function = self.extensions[function]
    extension_function.call(*args)
  else
    raise TypeError, "Extension function #{function} not recognized"
  end
end

.extension?(function) ⇒ Boolean

Is an extension function available?

It's either a registered extension, or an XSD casting function

Parameters:

  • function (RDF::URI)

Returns:

  • (Boolean)

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# File 'lib/sparql/algebra/expression.rb', line 180

def self.extension?(function)
  function.to_s.start_with?(RDF::XSD.to_s) || self.extensions[function]
end

.extensionsHash{RDF:URI: Proc}

Registered extensions

Returns:

  • (Hash{RDF:URI: Proc})

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# File 'lib/sparql/algebra/expression.rb', line 169

def self.extensions
  @extensions ||= {}
end

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

Examples:

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

Parameters:

  • sse (Array)

    a SPARQL S-Expression (SSE) form

Returns:


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# File 'lib/sparql/algebra/expression.rb', line 70

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

.new(sse, **options) ⇒ Expression

Examples:

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

Parameters:

Returns:

Raises:

  • (TypeError)

    if any of the operands is invalid


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# File 'lib/sparql/algebra/expression.rb', line 85

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)

  # If we don't find an operator, and sse.first is an extension IRI, use a function call
  if !operator && sse.first.is_a?(RDF::URI) && self.extension?(sse.first)
    operator = Operator.for(:function_call, sse.length)
    sse.unshift(:function_call)
  end

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

  operands = sse[1..-1].map do |operand|
    debug(options) {"Operator=#{operator.inspect}, Operand=#{operand.inspect}"}
    case operand
      when Array
        self.new(operand, depth: options[:depth].to_i + 1, **options)
      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(options) {"#{operator.inspect}(#{operands.map(&:inspect).join(',')})"}
  options.delete_if {|k, v| [:debug, :logger, :depth, :prefixes, :base_uri, :update, :validate].include?(k) }
  begin
    operator.new(*operands, **options)
  rescue ArgumentError => e
    error(options) {"Operator=#{operator.inspect}: #{e}"}
  end
end

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

Parses input from the given file name or URL.

Parameters:

Options Hash (**options):

  • :base_uri (RDF::URI, #to_s)

    Base URI used for loading relative URIs.

Yields:

  • (expression)

Yield Parameters:

Yield Returns:

  • (void)

    ignored

Returns:


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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.parse(file, **options, &block)
  end
end

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

Examples:

Expression.parse('(isLiteral 3.1415)')

Parameters:

  • sse (IO, String, #read, #to_s)

    a SPARQL S-Expression (SSE) string or IO object responding to #read

  • options (Hash{Symbol => Object})

    any additional options (see Operator#initialize)

Options Hash (**options):

  • :base_uri (RDF::URI, #to_s)

    Base URI used for loading relative URIs.

Yields:

  • (expression)

Yield Parameters:

Yield Returns:

  • (void)

    ignored

Returns:


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# File 'lib/sparql/algebra/expression.rb', line 24

def self.parse(sse, **options, &block)
  sse = sse.encode(Encoding::UTF_8)
  sxp = SXP::Reader::SPARQL.new(sse) do |reader|
    # Set base_uri if we have one
    reader.base_uri = options[:base_uri] if options[:base_uri]
  end
  sxp_result = sxp.read

  debug(options) {"base_uri: #{options[:base_uri]}"}
  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

.register_extension(uri) {|*args| ... }

This method returns an undefined value.

Register an extension function.

Extension functions take zero or more arguments of type RDF::Term and return an argument of type RDF::Term, or raise TypeError.

Functions are identified using the uri parameter and specified using a block.

Arguments are evaluated, and the block is called with argument values (if a variable was unbound, an error will have been generated).

It is possible to get unevaluated arguments but care must be taken not to violate the rules of function evaluation.

Normally, block should be a pure evaluation based on it's arguments. It should not access a graph nor return different values for the same arguments (to allow expression optimization). Blocks can't bind a variables.

Examples:

registering a function definition applying the Ruby crypt method to its unary argument.

SPARQL::Algebra::Expression.register_extension(RDF::URI("http://example/crypt") do |literal|
  raise TypeError, "argument must be a literal" unless literal.literal?
  RDF::Literal(literal.to_s.crypt("salt"))
end

Parameters:

  • uri (RDF::URI)

Yields:

  • *args

Yield Parameters:

Yield Returns:

Raises:

  • (TypeError)

    if uri is not an RDF::URI or no block is given


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# File 'lib/sparql/algebra/expression.rb', line 159

def self.register_extension(uri, &block)
  raise TypeError, "uri must be an IRI" unless uri.is_a?(RDF::URI)
  raise TypeError, "must pass a block" unless block_given?
  self.extensions[uri] = block
end

Instance Method Details

#constant?Boolean

Returns true.

Returns:

  • (Boolean)

    true or false

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 316

def constant?
  !(variable?)
end

#invalid?Boolean

Is this value invalid, or is it composed of any invalid components?

Returns:

  • (Boolean)

    true or false


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# File 'lib/sparql/algebra/expression.rb', line 371

def invalid?
  !valid?
end

#node?Boolean

Returns false.

Returns:

  • (Boolean)

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# File 'lib/sparql/algebra/expression.rb', line 307

def node?
  false
end

#optimize(**options) ⇒ Expression

Returns an optimized version of this expression.

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

Parameters:

  • options (Hash{Symbol => Object})

    any additional options for optimization

Returns:

See Also:

  • RDF::Query#optimize

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# File 'lib/sparql/algebra/expression.rb', line 331

def optimize(**options)
  self.deep_dup.optimize!(**options)
end

#optimize!(**options) ⇒ self

Optimizes this query.

Parameters:

  • options (Hash{Symbol => Object})

    any additional options for optimization

Returns:

  • (self)

See Also:

  • RDF::Query#optimize!

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# File 'lib/sparql/algebra/expression.rb', line 342

def optimize!(**options)
  self
end

#to_sxp_binArray

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.

Returns:

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 355

def to_sxp_bin
  self
end

#valid?Boolean

Is this value valid, and composed only of valid components?

Returns:

  • (Boolean)

    true or false


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# File 'lib/sparql/algebra/expression.rb', line 363

def valid?
  true
end

#validate!SPARQL::Algebra::Expression Also known as: validate

Default validate! implementation, overridden in concrete classes

Returns:

Raises:

  • (ArgumentError)

    if the value is invalid


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# File 'lib/sparql/algebra/expression.rb', line 379

def validate!
  raise ArgumentError if invalid?
  self
end

#variable?Boolean

Returns false.

Returns:

  • (Boolean)

    true or false

See Also:


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# File 'lib/sparql/algebra/expression.rb', line 299

def variable?
  false
end