# File lib/rdf/redland/schemas/rdfs.rb, line 49
  def add_label(a_label,lang=nil)
    label = Literal.new(a_label,lang)
    labels = self.get_properties(RDFS_LABEL) do |a_label| 
      if a_label.language == lang
        self.model.delete(self,RDFS_LABEL,a_label)
      end       
    end
    self.add_property(RDFS_LABEL,label)
    return self
  end