Abstract

We suggest a compositional vector representation of parse trees that relies on a recursive combination of recurrent-neural network encoders. To demonstrate its effectiveness, we use the representation as the backbone of a greedy, bottom-up dependency parser, achieving very strong accuracies for English and Chinese, without relying on external word embeddings. The parser’s implementation is available for download at the first author’s webpage.

Highlights

  • Dependency-based syntactic representations of sentences are central to many language processing tasks (Kübler et al, 2009)

  • Recurrent neural networks (RNNs) (Elman, 1990), and in particular methods based on the Long Short Term Memory (LSTM) architecture (Hochreiter and Schmidhuber, 1997), work very well for modeling sequences, and constantly obtain state-of-the-art results on both languagemodeling and prediction tasks (see, e.g. (Mikolov et al, 2010))

  • Our tree encoder uses recurrent neural networks as a building block: we model the left and right sequences of modifiers using RNNs, which are composed in a recursive manner to form a tree (Section 3)

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Summary

Introduction

Dependency-based syntactic representations of sentences are central to many language processing tasks (Kübler et al, 2009). Recurrent neural networks (RNNs) (Elman, 1990), and in particular methods based on the LSTM architecture (Hochreiter and Schmidhuber, 1997), work very well for modeling sequences, and constantly obtain state-of-the-art results on both languagemodeling and prediction tasks Recursive neural networks do not cope well with trees with arbitrary branching factors – most work require the encoded trees to be binary-branching, or have a fixed maximum arity. Our tree encoder uses recurrent neural networks as a building block: we model the left and right sequences of modifiers using RNNs, which are composed in a recursive manner to form a tree (Section 3). We use our tree representation for encoding the partially-built parse trees in a greedy, bottom-up dependency parser which is based on the easy-first transition-system of Goldberg and Elhadad (2010).

Dependency-based Representation
Recurrent Networks and LSTMs
A note on the head-outward generation
Bottom-up Parsing
Bottom-up Tree-Encoding
Labeled Tree Representation
Scoring Function
Computational Complexity
Loss and Parameter Updates
Error-Exploration and Dynamic Oracle Training
Out-of-vocabulary items and word-dropout
Implementation Details
Experiments and Results
Results
Related Work
Conclusions and Future Work
11: Call ADAM to minimize SumLoss

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