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Finding Function in Form: Compositional Character Models for Open Vocabulary Word Representation (1508.02096v2)

Published 9 Aug 2015 in cs.CL

Abstract: We introduce a model for constructing vector representations of words by composing characters using bidirectional LSTMs. Relative to traditional word representation models that have independent vectors for each word type, our model requires only a single vector per character type and a fixed set of parameters for the compositional model. Despite the compactness of this model and, more importantly, the arbitrary nature of the form-function relationship in language, our "composed" word representations yield state-of-the-art results in LLMing and part-of-speech tagging. Benefits over traditional baselines are particularly pronounced in morphologically rich languages (e.g., Turkish).

Citations (638)

Summary

  • The paper introduces a compositional character model using bidirectional LSTMs to generate efficient word representations.
  • It significantly reduces parameter count by composing vectors from character sequences, outperforming traditional word lookup methods.
  • Experimental results demonstrate superior performance in POS tagging and language modeling, especially for morphologically rich languages.

Compositional Character Models for Open Vocabulary Word Representation

The paper introduces a novel approach to word representation in the field of NLP by presenting a character-based compositional model that employs bidirectional Long Short-Term Memory networks (LSTMs). This method stands in contrast to traditional word representation models that rely on individual vectors for each word type.

Main Contributions

The authors propose a word embedding model that composes vector representations from character sequences instead of relying on large, independent word vectors. This approach significantly reduces the parameter space by requiring only a single vector per character type, complemented by a fixed set of parameters for the compositional model.

Methodology

Key aspects of the proposed model include:

  • Bidirectional LSTMs: Utilized to read character sequences and produce a composite vector representation for words. This technique leverages LSTMs’ ability to capture complex non-linear and non-local dynamics, allowing the model to understand both morphological processes and non-compositional word forms.
  • Compactness: The model's architecture results in a reduced number of parameters, facilitating efficiency without sacrificing performance.

Experimental Evaluation

The authors evaluate the compositional character model on LLMing and part-of-speech (POS) tagging tasks across various languages. Results demonstrate:

  1. State-of-the-art performance in POS tagging, notably surpassing previous benchmarks in English.
  2. Significant performance gains in morphologically rich languages such as Turkish, where traditional word-based models struggle due to extensive morphological variations.

Numerical Results

The model shows superior performance with fewer parameters. In the LLMing task, the compositional model consistently outperforms word lookup tables in several languages. The paramount efficiency is highlighted by achieving lower perplexity scores, particularly in languages with rich morphological structures.

Implications and Future Directions

The paper's findings implicate several practical and theoretical advancements:

  • Scalability: The proposed model's efficiency makes it viable for use in large-scale NLP applications, reducing computational overhead and memory usage.
  • Morphological Richness: By effectively capturing linguistic nuances in morphologically complex languages, the approach opens avenues for further research into language-specific adaptations and optimizations.
  • Open Vocabulary Systems: The potential to handle out-of-vocabulary and nonce words offers enhancements in various NLP tasks, suggesting broader adoption in open vocabulary systems.

Conclusion

This research contributes a robust methodology for word representation that possesses significant theoretical promise and practical applicability. Future exploration could delve into domain-specific adaptations and further optimize the balance between model complexity and performance. The integration of character-based compositional models might catalyze advancements in handling diverse linguistic phenomena and large-scale text processing.