Class: RDF::Literal

Inherits:
Object
  • Object
show all
Includes:
Term
Defined in:
lib/rdf/model/literal.rb,
lib/rdf/model/literal/date.rb,
lib/rdf/model/literal/time.rb,
lib/rdf/model/literal/token.rb,
lib/rdf/model/literal/double.rb,
lib/rdf/model/literal/boolean.rb,
lib/rdf/model/literal/decimal.rb,
lib/rdf/model/literal/integer.rb,
lib/rdf/model/literal/numeric.rb,
lib/rdf/model/literal/datetime.rb

Overview

An RDF literal.

Subclasses of Literal should define DATATYPE and GRAMMAR constants, which are used for identifying the appropriate class to use for a datatype URI and to perform lexical matching on the value.

Literal comparison with other Value instances call Value#type_error, which, returns false. Implementations wishing to have TypeError raised should mix-in TypeCheck. This is required for strict SPARQL conformance.

Specific typed literals may have behavior different from the default implementation. See the following defined sub-classes for specific documentation. Additional sub-classes may be defined, and will interoperate by defining DATATYPE and GRAMMAR constants, in addition other required overrides of RDF::Literal behavior.

In RDF 1.1, all literals are typed, including plain literals and language tagged literals. Internally, plain literals are given the xsd:string datatype and language tagged literals are given the rdf:langString datatype. Creating a plain literal, without a datatype or language, will automatically provide the xsd:string datatype; similar for language tagged literals. Note that most serialization formats will remove this datatype. Code which depends on a literal having the xsd:string datatype being different from a plain literal (formally, without a datatype) may break. However note that the #has\_datatype? will continue to return false for plain or language-tagged literals.

Examples:

Creating a plain literal

value = RDF::Literal.new("Hello, world!")
value.plain?                                   #=> true`

Creating a language-tagged literal (1)

value = RDF::Literal.new("Hello!", language: :en)
value.language?                                #=> true
value.language                                 #=> :en

Creating a language-tagged literal (2)

RDF::Literal.new("Wazup?", language: :"en-US")
RDF::Literal.new("Hej!",   language: :sv)
RDF::Literal.new("¡Hola!", language: :es)

Creating an explicitly datatyped literal

value = RDF::Literal.new("2009-12-31", datatype: RDF::XSD.date)
value.datatype?                                #=> true
value.datatype                                 #=> RDF::XSD.date

Creating an implicitly datatyped literal

value = RDF::Literal.new(Date.today)
value.datatype?                                #=> true
value.datatype                                 #=> RDF::XSD.date

Creating implicitly datatyped literals

RDF::Literal.new(false).datatype               #=> XSD.boolean
RDF::Literal.new(true).datatype                #=> XSD.boolean
RDF::Literal.new(123).datatype                 #=> XSD.integer
RDF::Literal.new(9223372036854775807).datatype #=> XSD.integer
RDF::Literal.new(3.1415).datatype              #=> XSD.double
RDF::Literal.new(Time.now).datatype            #=> XSD.dateTime
RDF::Literal.new(Date.new(2010)).datatype      #=> XSD.date
RDF::Literal.new(DateTime.new(2010)).datatype  #=> XSD.dateTime

See Also:

Direct Known Subclasses

Boolean, Date, DateTime, Numeric, Time, Token

Defined Under Namespace

Classes: Boolean, Date, DateTime, Decimal, Double, Integer, Numeric, Time, Token

Constant Summary collapse

TRUE =
RDF::Literal.new(true)
FALSE =
RDF::Literal.new(false)
ZERO =
RDF::Literal.new(0)

Instance Attribute Summary collapse

Instance Method Summary collapse

Methods included from Term

#term?, #terms, #to_base, #to_term

Methods included from Value

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

Constructor Details

#initialize(value, language: nil, datatype: nil, lexical: nil, validate: false, canonicalize: false, **options) ⇒ Literal

Literals without a datatype are given either xsd:string or rdf:langString depending on if there is language

Parameters:

  • value (Object)
  • language (Symbol) (defaults to: nil)

    (nil) Language is downcased to ensure proper matching

  • lexical (String) (defaults to: nil)

    (nil) Supplied lexical representation of this literal, otherwise it comes from transforming value to a string form..

  • datatype (URI) (defaults to: nil)

    (nil)

  • validate (Boolean) (defaults to: false)

    (false)

  • canonicalize (Boolean) (defaults to: false)

    (false)

Raises:

  • (ArgumentError)

    if there is a language and datatype is no rdf:langString or datatype is rdf:langString and there is no language

See Also:


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# File 'lib/rdf/model/literal.rb', line 165

def initialize(value, language: nil, datatype: nil, lexical: nil, validate: false, canonicalize: false, **options)
  @object   = value.freeze
  @string   = lexical if lexical
  @string   = value if !defined?(@string) && value.is_a?(String)
  @string   = @string.encode(Encoding::UTF_8).freeze if @string
  @object   = @string if @string && @object.is_a?(String)
  @language = language.to_s.downcase.to_sym if language
  @datatype = RDF::URI(datatype).freeze if datatype
  @datatype ||= self.class.const_get(:DATATYPE) if self.class.const_defined?(:DATATYPE)
  @datatype ||= @language ? RDF.langString : RDF::URI("http://www.w3.org/2001/XMLSchema#string")
end

Dynamic Method Handling

This class handles dynamic methods through the method_missing method

#String (protected)

This method is implemented when the datatype is xsd:string or rdf:langString

Returns:


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# File 'lib/rdf/model/literal.rb', line 546

def method_missing(name, *args)
  case name
  when :to_str
    return to_s if @datatype == RDF.langString || @datatype == RDF::URI("http://www.w3.org/2001/XMLSchema#string")
  end
  super
end

Instance Attribute Details

#datatypeURI

Returns The XML Schema datatype URI (optional).

Returns:

  • (URI)

    The XML Schema datatype URI (optional).


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# File 'lib/rdf/model/literal.rb', line 144

def datatype
  @datatype
end

#languageSymbol

Returns The language tag (optional).

Returns:

  • (Symbol)

    The language tag (optional).


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# File 'lib/rdf/model/literal.rb', line 141

def language
  @language
end

Instance Method Details

#<=>(other) ⇒ Integer

Compares self to other for sorting purposes (with type check).

Parameters:

  • other (Object)

Returns:


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# File 'lib/rdf/model/literal.rb', line 316

def <=>(other)
  case other
  when Literal
    case
    when self.eql?(other)
      0
    when self.language? && other.language?
      # Literals with languages can compare if languages are identical
      self.to_s <=> other.to_s
    when self.simple? && other.simple?
      self.to_s <=> other.to_s
    when !self.valid?
      type_error("#{self.inspect} is invalid") || 0
    when !other.valid?
      type_error("#{other.inspect} is invalid") || 0
    when self.comperable_datatype2?(other)
      self.object <=> other.object
    else
      type_error("#{self.inspect} and #{other.inspect} are not comperable") || 0
    end
  when String
    self.simple? && self.value <=> other
  else 1
  end
end

#==(other) ⇒ Boolean Also known as: ===

Returns true if this literal is equivalent to other (with type check).

Examples:

RDF::Literal(1) == RDF::Literal(1.0)     #=> true

Parameters:

  • other (Object)

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 286

def ==(other)
  case other
  when Literal
    case
    when self.eql?(other)
      true
    when self.language? && self.language.to_s == other.language.to_s
      # Literals with languages can compare if languages are identical
      self.value_hash == other.value_hash && self.value == other.value
    when self.simple? && other.simple?
      self.value_hash == other.value_hash && self.value == other.value
    when other.comperable_datatype?(self) || self.comperable_datatype?(other)
      # Comoparing plain with undefined datatypes does not generate an error, but returns false
      # From data-r2/expr-equal/eq-2-2.
      false
    else
      type_error("unable to determine whether #{self.inspect} and #{other.inspect} are equivalent")
    end
  when String
    self.simple? && self.value.eql?(other)
  else false
  end
end

#canonicalize!RDF::Literal

Converts this literal into its canonical lexical representation.

Subclasses should override this as needed and appropriate.

Returns:

Since:

  • 0.3.0


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# File 'lib/rdf/model/literal.rb', line 466

def canonicalize!
  self
end

#compatible?(other) ⇒ Boolean

Term compatibility according to SPARQL

Compatibility of two arguments is defined as:

  • The arguments are simple literals or literals typed as xsd:string
  • The arguments are plain literals with identical language tags
  • The first argument is a plain literal with language tag and the second argument is a simple literal or literal typed as xsd:string

Examples:

compatible?("abc"	"b")                         #=> true
compatible?("abc"	"b"^^xsd:string)             #=> true
compatible?("abc"^^xsd:string	"b")             #=> true
compatible?("abc"^^xsd:string	"b"^^xsd:string) #=> true
compatible?("abc"@en	"b")                     #=> true
compatible?("abc"@en	"b"^^xsd:string)         #=> true
compatible?("abc"@en	"b"@en)                  #=> true
compatible?("abc"@fr	"b"@ja)                  #=> false
compatible?("abc"	"b"@ja)                      #=> false
compatible?("abc"	"b"@en)                      #=> false
compatible?("abc"^^xsd:string	"b"@en)          #=> false

Returns:

See Also:

Since:

  • 2.0


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# File 'lib/rdf/model/literal.rb', line 222

def compatible?(other)
  return false unless other.literal? && plain? && other.plain?

  # * The arguments are simple literals or literals typed as xsd:string
  # * The arguments are plain literals with identical language tags
  # * The first argument is a plain literal with language tag and the second argument is a simple literal or literal typed as xsd:string
  language? ?
    (language == other.language || other.datatype == RDF::URI("http://www.w3.org/2001/XMLSchema#string")) :
    other.datatype == RDF::URI("http://www.w3.org/2001/XMLSchema#string")
end

#comperable_datatype2?(other) ⇒ Boolean

Returns true if the literal has a datatype and the comparison should return false instead of raise a type error.

Used for <=> operator.

This behavior is intuited from SPARQL data-r2/expr-equal/eq-2-2

Returns:


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# File 'lib/rdf/model/literal.rb', line 441

def comperable_datatype2?(other)
  case self
  when RDF::Literal::Numeric, RDF::Literal::Boolean
    case other
    when RDF::Literal::Numeric, RDF::Literal::Boolean
      true
    else
      self.plain? || other.plain? ||
      self.language? || other.language? ||
      self.datatype == other.datatype
    end
  else
    self.plain? || other.plain? ||
    self.language? || other.language? ||
    self.datatype == other.datatype
  end
end

#comperable_datatype?(other) ⇒ Boolean

Returns true if the literal has a datatype and the comparison should return false instead of raise a type error.

This behavior is intuited from SPARQL data-r2/expr-equal/eq-2-2

Returns:


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# File 'lib/rdf/model/literal.rb', line 419

def comperable_datatype?(other)
  return false unless self.plain? || self.language?

  case other
  when RDF::Literal::Numeric, RDF::Literal::Boolean,
       RDF::Literal::Date, RDF::Literal::Time, RDF::Literal::DateTime
    # Invald types can be compared without raising a TypeError if literal has a language (open-eq-08)
    !other.valid? && self.language?
  else
    # An unknown datatype may not be used for comparison, unless it has a language? (open-eq-8)
    self.language?
  end
end

#datatype?Boolean Also known as: has_datatype?, typed?, datatyped?

Returns true if this is a datatyped literal.

For historical reasons, this excludes xsd:string and rdf:langString

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 381

def datatype?
  !plain? && !language?
end

#eql?(other) ⇒ Boolean

Determins if self is the same term as other.

Examples:

RDF::Literal(1).eql?(RDF::Literal(1.0))  #=> false

Parameters:

  • other (Object)

Returns:


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# File 'lib/rdf/model/literal.rb', line 266

def eql?(other)
  self.equal?(other) ||
    (self.class.eql?(other.class) &&
     self.value_hash == other.value_hash &&
     self.value.eql?(other.value) &&
     self.language.to_s.eql?(other.language.to_s) &&
     self.datatype.eql?(other.datatype))
end

#escape(string) ⇒ String

Note:

N-Triples only requires '\"\n\r' to be escaped.

Escape a literal using ECHAR escapes.

ECHAR ::= '\' [tbnrf"']

Parameters:

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 504

def escape(string)
  string.gsub('\\', '\\\\').
         gsub("\t", '\\t').
         gsub("\b", '\\b').
         gsub("\n", '\\n').
         gsub("\r", '\\r').
         gsub("\f", '\\f').
         gsub('"', '\\"').
         freeze
end

#hashInteger

Returns a hash code for this literal.

Returns:


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# File 'lib/rdf/model/literal.rb', line 237

def hash
  @hash ||= [to_s, datatype, language].hash
end

#humanize(lang = :en) ⇒ String

Returns a human-readable value for the literal

Returns:

Since:

  • 1.1.6


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# File 'lib/rdf/model/literal.rb', line 528

def humanize(lang = :en)
  to_s.freeze
end

#inspectString

Returns a developer-friendly representation of self.

Returns:


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# File 'lib/rdf/model/literal.rb', line 536

def inspect
  sprintf("#<%s:%#0x(%s)>", self.class.name, __id__, RDF::NTriples.serialize(self))
end

#language?Boolean Also known as: has_language?

Returns true if this is a language-tagged literal.

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 369

def language?
  datatype == RDF.langString
end

#literal?Boolean

Returns true.

Returns:


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# File 'lib/rdf/model/literal.rb', line 195

def literal?
  true
end

#objectObject

Returns:

  • (Object)

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# File 'lib/rdf/model/literal.rb', line 187

def object
  defined?(@object) ? @object : value
end

#plain?Boolean

Returns true if this is a plain literal. A plain literal may have a language, but may not have a datatype. For all practical purposes, this includes xsd:string literals too.

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 350

def plain?
  [RDF.langString, RDF::URI("http://www.w3.org/2001/XMLSchema#string")].include?(datatype)
end

#respond_to_missing?(name, include_private = false) ⇒ Boolean (protected)

Returns:


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# File 'lib/rdf/model/literal.rb', line 554

def respond_to_missing?(name, include_private = false)
  case name
  when :to_str
    return true if @datatype == RDF.langString || @datatype == RDF::URI("http://www.w3.org/2001/XMLSchema#string")
  end
  super
end

#simple?Boolean

Returns true if this is a simple literal. A simple literal has no datatype or language.

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 360

def simple?
  datatype == RDF::URI("http://www.w3.org/2001/XMLSchema#string")
end

#squish(*other_string) ⇒ RDF::Literal

Returns the literal, first removing all whitespace on both ends of the value, and then changing remaining consecutive whitespace groups into one space each.

Note that it handles both ASCII and Unicode whitespace.

Returns:

See Also:


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# File 'lib/rdf/model/literal.rb', line 477

def squish(*other_string)
  self.dup.squish!
end

#squish!Object

Performs a destructive #squish.


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# File 'lib/rdf/model/literal.rb', line 486

def squish!
  @string = value.
    gsub(/\A[[:space:]]+/, '').
    gsub(/[[:space:]]+\z/, '').
    gsub(/[[:space:]]+/, ' ')
  self
end

#to_sString

Returns the value as a string.

Returns:


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# File 'lib/rdf/model/literal.rb', line 519

def to_s
  @object.to_s.freeze
end

#valid?Boolean

Returns true if the value adheres to the defined grammar of the datatype.

Returns:

Since:

  • 0.2.1


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# File 'lib/rdf/model/literal.rb', line 394

def valid?
  return false if language? && language.to_s !~ /^[a-zA-Z]{1,8}(-[a-zA-Z0-9]{1,8})*$/
  return false if datatype? && datatype.invalid?
  grammar = self.class.const_get(:GRAMMAR) rescue nil
  grammar.nil? || value.match?(grammar)
end

#validate!RDF::Literal

Validates the value using Value#valid?, raising an error if the value is invalid.

Returns:

Raises:

  • (ArgumentError)

    if the value is invalid

Since:

  • 0.2.1


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# File 'lib/rdf/model/literal.rb', line 408

def validate!
  raise ArgumentError, "#{to_s.inspect} is not a valid <#{datatype.to_s}> literal" if invalid?
  self
end

#valueString

Returns the value as a string.

Returns:


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# File 'lib/rdf/model/literal.rb', line 181

def value
  @string || to_s
end

#value_hashInteger

Returns a hash code for the value.

Returns:


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# File 'lib/rdf/model/literal.rb', line 246

def value_hash
  @value_hash ||= value.hash
end