Story Realization: Expanding Plot Events into Sentences
Summary
The paper addresses automated plot generation in which a story is first built as a sequence of abstract "events," and each event is then turned into a natural-language sentence. This second stage is called event-to-sentence. On this task, ordinary sequence-to-sequence LSTMs often behave like plain language models: they produce grammatical sentences that have little to do with the content of the input event. This happens because the data are sparse and because newly generated events were never seen during training. The authors propose an ensemble of four models plus a fallback seq2seq. Each model strikes its own balance between preserving the event's content and making the text interesting. If a model's confidence does not reach its threshold, the event is passed to the next model. The ensemble is built into a full story-generation pipeline together with a reinforcement-learning-based event-to-event module. The ensemble achieves lower perplexity than any individual model. Survey participants rated its stories higher than those of the baseline model for grammaticality, genre adherence, and reading enjoyment. The work shows how to achieve semantically controlled text generation from an abstract plan.
Key points
- An event is a 5-tuple ⟨s, v, o, p, m⟩: subject, verb, object, preposition, and modifier. Verbs are generalized to VerbNet v3.3 classes, and nouns to WordNet v3.1 Synsets two levels up the hypernym hierarchy. Named entities are numbered with tags such as <PERSON>0.
- The order of models in the ensemble is: retrieve-and-edit (following Hashimoto et al. 2018), sentence templates, seq2seq with Monte Carlo beam decoding, seq2seq with a finite-state machine (FSM) as the decoder, and finally a standard beam-search seq2seq as the fallback.
- The RetEdit model performs best on test events. For events generated within the pipeline it is used much less often: in the RetEdit+MC combination, 82.58% versus 31.74%. Most of these events are picked up by Monte Carlo beam search.
- In an Amazon Mechanical Turk study, stories were rated on a 5-point Likert scale; the genre was space opera. After filtering, 64 participants remained for the ensemble and 58 for the baseline model. The advantage in reading enjoyment and genre adherence is statistically significant only at the p < 0.10 level.
- The event-to-event module is policy gradient RL from Tambwekar et al. (2019). The code is published on GitHub: rajammanabrolu/StoryRealization.
Cite
@misc{ammanabrolu2019story,
title = {{Story Realization: Expanding Plot Events into Sentences}},
author = {Ammanabrolu, Prithviraj and Tien, Ethan and Cheung, Wesley and Luo, Zhaochen and Ma, William and Martin, Lara J. and Riedl, Mark O.},
year = {2019},
doi = {10.1609/aaai.v34i05.6232},
eprint = {1909.03480},
archivePrefix = {arXiv},
url = {https://doi.org/10.1609/aaai.v34i05.6232}
}References
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