module SPARQL::Algebra::Expression

A SPARQL algebra expression.

@abstract

Public Class Methods

[](*sse)
Alias for: for
cast(datatype, value) click to toggle source

Casts operand as the specified datatype

@param [RDF::URI] datatype

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

@param [RDF::Term] value

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

@raise [TypeError] if datatype is not a URI or value cannot be cast to datatype @return [RDF::Term] @see www.w3.org/TR/sparql11-query/#FunctionMapping

# File lib/sparql/algebra/expression.rb, line 199
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) click to toggle source

Invoke an extension function.

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

@param [RDF::URI] function @param [Array<RDF::Term>] args splat of args to function @return [RDF::Term] @see www.w3.org/TR/sparql11-query/#extensionFunctions @see www.w3.org/TR/sparql11-query/#FunctionMapping

# File lib/sparql/algebra/expression.rb, line 178
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
extensions() click to toggle source

Registered extensions

@return [Hash{RDF:URI: Proc}]

# File lib/sparql/algebra/expression.rb, line 162
def self.extensions
  @extensions ||= {}
end
for(*sse) click to toggle source

@example

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

@param [Array] sse

a SPARQL S-Expression (SSE) form

@return [Expression]

# File lib/sparql/algebra/expression.rb, line 70
def self.for(*sse)
  self.new(sse)
end
Also aliased as: []
new(sse, **options) click to toggle source

@example

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

@param [Array] sse

a SPARQL S-Expression (SSE) form

@param [Hash{Symbol => Object}] options

any additional options (see {Operator#initialize})

@return [Expression] @raise [TypeError] if any of the operands is invalid

# 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)
  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, &block) click to toggle source

Parses input from the given file name or URL.

@param [String, to_s] filename @param [Hash{Symbol => Object}] options

any additional options (see {Operator#initialize})

@option options [RDF::URI, to_s] :base_uri

Base URI used for loading relative URIs.

@yield [expression] @yieldparam [SPARQL::Algebra::Expression] expression @yieldreturn [void] ignored @return [Expression]

# 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| ... } click to toggle source

@example

Expression.parse('(isLiteral 3.1415)')

@param [IO, String, read, to_s] sse

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

@param [Hash{Symbol => Object}] options

any additional options (see {Operator#initialize})

@option options [RDF::URI, to_s] :base_uri

Base URI used for loading relative URIs.

@yield [expression] @yieldparam [SPARQL::Algebra::Expression] expression @yieldreturn [void] ignored @return [Expression]

# 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, &block) click to toggle source

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.

@example 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

@param [RDF::URI] uri @yield *args @yieldparam [Array<RDF::Term>] *args @yieldreturn [RDF::Term] @return [void] @raise [TypeError] if `uri` is not an RDF::URI or no block is given

# File lib/sparql/algebra/expression.rb, line 152
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

Private Class Methods

debug(*args, &block) click to toggle source

@overload: May be called with node, message and an option hash

@param [String] node processing node
@param [String] message
@param [Hash{Symbol => Object}] options
@option options [Logger] :logger for logging progress
@option options [Integer] :depth (@productions.length)
  Processing depth for indenting message output.
@yieldreturn [String] appended to message, to allow for lazy-evaulation of message

@overload: May be called with node and an option hash

@param [String] node processing node
@param [Hash{Symbol => Object}] options
@option options [Logger] :logger for logging progress
@option options [Integer] :depth (@productions.length)
  Processing depth for indenting message output.
@yieldreturn [String] appended to message, to allow for lazy-evaulation of message

@overload: May be called with only options, in which case the block is used to return the output message

@param [String] node processing node
@param [Hash{Symbol => Object}] options
@option options [Logger] :logger for logging progress
@option options [Integer] :depth (@productions.length)
  Processing depth for indenting message output.
@yieldreturn [String] appended to message, to allow for lazy-evaulation of message
# File lib/sparql/algebra/expression.rb, line 408
def self.debug(*args, &block)
  options = args.last.is_a?(Hash) ? args.pop : {}
  return unless options[:logger]
  options[:logger].debug(*args, **options, &block)
end

Public Instance Methods

constant?() click to toggle source

Returns `true`.

@return [Boolean] `true` or `false` @see variable?

# File lib/sparql/algebra/expression.rb, line 298
def constant?
  !(variable?)
end
evaluate(bindings, **options) click to toggle source

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.

@param [RDF::Query::Solution] bindings

a query solution containing zero or more variable bindings

@param [Hash{Symbol => Object}] options ({})

options passed from query

@return [Expression] `self`

# File lib/sparql/algebra/expression.rb, line 340
def evaluate(bindings, **options)
  self
end
invalid?() click to toggle source

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

@return [Boolean] `true` or `false`

# File lib/sparql/algebra/expression.rb, line 369
def invalid?
  !valid?
end
node?() click to toggle source

Returns `false`.

@return [Boolean]

# File lib/sparql/algebra/expression.rb, line 289
def node?
  false
end
optimize(**options) click to toggle source

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.

@param [Hash{Symbol => Object}] options

any additional options for optimization

@return [Expression] a copy of `self` @see RDF::Query#optimize

# File lib/sparql/algebra/expression.rb, line 313
def optimize(**options)
  self.deep_dup.optimize!(**options)
end
optimize!(**options) click to toggle source

Optimizes this query.

@param [Hash{Symbol => Object}] options

any additional options for optimization

@return [self] @see RDF::Query#optimize!

# File lib/sparql/algebra/expression.rb, line 324
def optimize!(**options)
  self
end
to_sxp_bin() click to toggle source

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.

@return [Array] `self` @see openjena.org/wiki/SSE

# File lib/sparql/algebra/expression.rb, line 353
def to_sxp_bin
  self
end
valid?() click to toggle source

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

@return [Boolean] `true` or `false`

# File lib/sparql/algebra/expression.rb, line 361
def valid?
  true
end
validate()
Alias for: validate!
validate!() click to toggle source

Default validate! implementation, overridden in concrete classes @return [SPARQL::Algebra::Expression] `self` @raise [ArgumentError] if the value is invalid

# File lib/sparql/algebra/expression.rb, line 377
def validate!
  raise ArgumentError if invalid?
  self
end
Also aliased as: validate
variable?() click to toggle source

Returns `false`.

@return [Boolean] `true` or `false` @see variable?

# File lib/sparql/algebra/expression.rb, line 281
def variable?
  false
end

Private Instance Methods

debug(*args, &block) click to toggle source
# File lib/sparql/algebra/expression.rb, line 414
def debug(*args, &block)
  options = args.last.is_a?(Hash) ? args.pop : {}
  log_debug(*args, **options, &block)
end