'Return a dependency graph for the sentence.
:param sentence: the sentence to be parsed
:type sentence: list(str)
:rtype: DependencyGraph'

def dep_parse(self, sentence):

    if (self.depparser is None):
        from nltk.parse import MaltParser
        self.depparser = MaltParser(tagger=self.get_pos_tagger())
    if (not self.depparser._trained):
        self.train_depparser()
    return self.depparser.parse(sentence, verbose=self.verbose)
