Open-domain utterance generation using phrase pairs based on dependency relations

The development of open-domain conversational systems remains difficult since user utterances are widely varied for such systems to respond appropriately. To address this is- sue, previous research has retrieved sentences from the web as system utterances by shallow sentence matching with user utterances. However, since the retrieved sentences include the inherent contexts of the document in which the sentences originally appeared, the retrieved sentences have the possibility of containing information that is irrelevant to user utter-ances. We propose combining two strongly related semantic units (phrase pairs with dependency relations) to create a system utterance. Here, the first semantic unit is the one found in the user utterance and the second semantic unit is the one that has a dependency relation with the first one in a large text cor- pus. This way, we can guarantee that the generated utterance is related to the input user utterance. Our experiments, which examine the appropriateness of response sentences, show that our proposed method significantly outperforms other retrieval and rule-based approaches.