Speech Act Modeling of Written Asynchronous Conversations with Task-Specific Embeddings and Conditional Structured Models
Summary
The paper addresses sentence-level speech act tagging in written asynchronous conversations such as forum threads and emails. In these threads, posts are not strictly sequential, and reply-to structure is often missing. Earlier systems tend to rely on sparse bag-of-words features and label each sentence independently. The authors propose a two-stage framework instead. First, an LSTM recurrent network, either unidirectional or bidirectional, with random or word2vec initialization, builds task-specific sentence embeddings that capture word order. Second, a pairwise Conditional Random Field over an arbitrary conversation graph uses these embeddings to label all sentences jointly. Several graph designs model links within and across comments, and inference uses loopy belief propagation. Models were trained on both synchronous and asynchronous corpora, and evaluation used a pair of forum datasets that includes the newly released QC3 corpus. LSTM encodings outperform BOW features, and bidirectional encoders beat unidirectional ones. Joint CRF models improve on local classifiers, but only when the graph structure fits the conversation. This matters for downstream uses such as thread summarization and question answering.
Key points
- Labels include Statement, Question, Suggestion, Polite and Response, following a standard speech act tagset. Evaluation uses two forum datasets, QC3 and TA.
- A new forum corpus, QC3, annotated with speech acts, was released together with source code at alt.qcri.org/tools/speech-act/.
- A plain linear-chain CRF in temporal order (CRF(LC-LC)) gives little gain. CRF(LC-LC1), which chains sentences inside each comment and links them to the first comment, significantly beats the local B-LSTM_p classifier at 99% confidence.
- Connecting to every sentence of the first comment (CRF(LC-FC1)) lowers performance. A fully connected CRF(FC-FC) performs on par with the best model.
- LSTM representations need more training data. Future work aims to train the LSTM and CRF end-to-end and to exploit explicit thread structure, such as email quotation graphs.
Cited by
Cite
@inproceedings{joty2016speech,
title = {{Speech Act Modeling of Written Asynchronous Conversations with Task-Specific Embeddings and Conditional Structured Models}},
author = {Joty, Shafiq and Hoque, Enamul},
booktitle = {Proceedings of the 54th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)},
year = {2016},
doi = {10.18653/v1/p16-1165},
url = {https://doi.org/10.18653/v1/p16-1165}
}References
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