@abstractmethod<EOL><INDENT>def segment(self, source, language=None):<DEDENT>
raise NotImplementedError()<EOL>
Returns a chunk list from the given sentence.

        Args:
          source (str): Source string to segment.
          language (:obj:`str`, optional): A language code.

        Returns:
          A chunk list. (:obj:`budou.chunk.ChunkList`)

        Raises:
          NotImplementedError: If not implemented.