class ToolParser
  def to_json
    self.to_json
  end

  def to_hash # or attributes
    self.to_hash
  end

  def execute(xml)
    raise NotImplementedError # do the hard work here
  end
end

class NessusParser < ToolParser
  def execute(xml)
    # do the hard work here and few other places :)
  end
end

class NmapParser < ToolParser
  def execute(xml)
    # do the hard work here and few other places :)
  end
end