Link to paper: https://arxiv.org/abs/2307.06962
Paper published on: 2023-07-13
Paper's authors: Tian Lan, Deng Cai, Yan Wang, Heyan Huang, Xian-Ling Mao
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The TLDR:
- COG is a new text generation model that selects phrases instead of individual words.
- It uses a deep bidirectional Transformer and MLP models to generate text.
- COG can adapt to new knowledge sources without needing extra training.
- It outperforms other models in terms of generation quality.
- It can generate multi-word phrases in one step, making it faster.
- It has been tested on different datasets and performs well.
- It could be used to make better chatbots, translations, and adapt to new topics quickly.
The Deeper Dive:
Understanding the New Text Generation Model: COG
In the realm of text generation, most models select words from a fixed vocabulary. However, the research we're discussing today proposes a new approach: copying text segments from existing text collections. This model, known as COG (COPY-GENERATOR), selects phrases in specific contexts instead of standalone tokens in a fixed vocabulary. This allows for a more accurate representation and selection.
Let's delve into the specifics of this model and how it outperforms standard baselines in terms of generation quality.
The COG Model: An Overview
COG, short for COPY-GENERATOR, is a retrieval-based text generation model that uses a phrase index for generating coherent and fluent text continuations. Unlike traditional models that use a fixed vocabulary, COG replaces this with a nonparametric phrase table.
The model uses a deep bidirectional Transformer to obtain contextualized token representations. Two MLP models, MLPstart and MLPend, are used to convert the token representations into start and end token representations. The phrase representations are obtained by concatenating the start and end vectors.
COG decomposes the task of text generation into a series of copy-and-paste operations. A greedy segmentation algorithm based on forward maximum matching is used to chunk the documents into phrases. COG uses a shared vector space of prefix and phrase representations, and the training loss for next-phrase predictions is defined using the InfoNCE loss with in-batch negatives.
Advantages of COG
The COG model has a number of advantages over traditional text generation models. For one, it allows for training-free adaptation to new knowledge sources by updating the text collection. This can benefit domain adaptation and data expansion/filtering. Moreover, COG allows for generating multi-word phrases in a single step, reducing the number of decoding steps and improving inference efficiency.
In terms of performance, COG outperforms standard baselines in terms of generation quality according to both automatic and human evaluations. It also performs well in domain adaptation settings and achieves additional performance gains when scaled up to larger text collections.
Experimental Results
Experiments were conducted on three benchmarks: WikiText-103, English part of Law-MT, and En-Wiki. The En-Wiki corpus used in the experiments contains over 4,848,348 long English Wikipedia documents.
The dynamic vocabulary of COG during training includes word-level vocabulary size and phrases in a batch of training documents. During inference, the dynamic vocabulary consists of word-level vocabulary and phrases extracted from the top-k retrieved documents. The pre-defined word-level vocabulary contains 50257 subwords.
The average number of phrase representations in the WikiText-103 test set is 950,942.4 when k=1024. The perplexity of generated texts under the COG model is compared to other models and the ground-truth, with COG achieving a perplexity score closest to the ground-truth.
Implications and Potential Applications
The COG model has the potential to revolutionize text generation. By selecting phrases in specific contexts, it allows for a more accurate representation and selection. This could be used to create more natural-sounding chatbots, or to generate more accurate translations.
In addition, the model's ability to adapt to new knowledge sources without additional training could be used to quickly and efficiently adapt a system to new domains or topics. This could be particularly useful in fields where new information is constantly being generated, such as news or scientific research.
Finally, the model's efficiency in generating multi-word phrases could be used to speed up text generation tasks, potentially making real-time text generation a reality.
