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Exact Hard Monotonic Attention for Character-Level Transduction

Published 1 January 2019Open access
Shijie Wu, Ryan Cotterell
Citations54
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TL;DR

This work develops a hard attention sequence-to-sequence model that enforces strict monotonicity and learns alignment jointly and achieves state-of-the-art performance on morphological inflection.

Abstract

Many common character-level, string-to-string transduction tasks, e.g., grapheme-to-phoneme conversion and morphological inflection, consist almost exclusively of monotonic transduction. Neural sequence-to-sequence models with soft attention, non-monotonic models, outperform popular monotonic models. In this work, we ask the following question: Is monotonicity really a helpful inductive bias in these tasks? We develop a hard attention sequence-to-sequence model that enforces strict monotonicity and learns alignment jointly. With the help of dynamic programming, we are able to compute the exact marginalization over all alignments. Our models achieve state-of-the-art performance on morphological inflection. Furthermore, we find strong performance on two other character-level transduction tasks. Code is available at https://github.com/shijie-wu/neural-transducer.

Keywords

Computer Science