Question: What problem does the paper want to address?
Evidence: Human-computer dialog/conversation is one of the most challenging problems in artificial intelligence. Given a user-issued utterance (called a query in this paper), the computer needs to provide a reply to the query. In early years, researchers have developed various domain-oriented dialogue systems, which are typically based on rules or templates BIBREF4 , BIBREF5 , BIBREF6 . Recently, open-domain conversation systems have attracted more and more attention in both academia and industry (e.g., XiaoBing from Microsoft and DuMi from Baidu). Due to high diversity, we can hardly design rules or templates in the open domain. Researchers have proposed information retrieval methods BIBREF7 and modern generative neural networks BIBREF8 , BIBREF9 to either search for a reply from a large conversation corpus or generate a new sentence as the reply.
In open-domain conversations, context information (one or a few previous utterances) is particularly important to language understanding BIBREF1 , BIBREF9 , BIBREF10 , BIBREF11 . As dialogue sentences are usually casual and short, a single utterance (e.g., “Thank you.” in Figure FIGREF2 ) does not convey much meaning, but its previous utterance (“...writing an essay”) provides useful background information of the conversation. Using such context will certainly benefit the conversation system.
However, tracking all previous utterances as the context is unwise. First, commercial chat-bots usually place high demands on efficiency. In a retrieval-based system, for example, performing a standard process of candidate retrieval and re-ranking for each previous utterance may well exceed the time limit (which is very short, e.g., 500ms). Second, we observe that not all sentences in the current conversation session are equally important. The sentence “Want to take a walk?” is irrelevant to the current context, and should not be considered when the computer synthesizes the reply. Therefore, it raises the question of session segmentation in conversation systems.
Document segmentation for general-purpose corpora has been widely studied in NLP. For example, Hearst BIBREF12 proposes the TextTiling approach; she measures the similarity of neighboring sentences based on bag-of-words features, and performs segmentation by thresholding. However, such approaches are not tailored to the dialogue genre and may not be suitable for conversation session segmentation.
In this paper, we address the problem of session segmentation for open-domain conversations. We leverage the classic TextTiling approach, but enhance it with modern embedding-based similarity measures. Compared with traditional bag-of-words features, embeddings map discrete words to real-valued vectors, capturing underlying meanings in a continuous vector space; hence, it is more robust for noisy conversation corpora. Further, we propose a tailored method for word embedding learning. In traditional word embedding learning, the interaction between two words in a query and a reply is weaker than that within an utterance. We propose to combine a query and its corresponding reply as a “virtual sentence,” so that it provides a better way of modeling utterances between two agents.
In this paper, we address the problem of session segmentation for open-domain conversations.
Answer: The problem of session segmentation in open-domain conversations.