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In this chapter, we implement a machine translation application as an example of an encoder-decoder task. In particular, we build on pretrained encoder-decoder transformer models, which exist in the Hugging Face library for a wide variety of language pairs. We first show how to use one of these models out-of-the-box to perform translation for one of the language pairs it has been exposed to during pretraining: English to Romanian. Afterward, we fine-tune the model to a new language combination that is has not seen before: Romanian to English. In both use cases, we use the T5 encoder-decoder model, which has been pretrained for several tasks, including machine translation.
So far we have explored classifiers with decision boundaries that are linear, or, in the case of the multiclass logistic regression, a combination of linear segments. In this chapter, we will expand what we have learned so far to classifiers that are capable of learning nonlinear decision boundaries. The classifiers that we will discuss here are called feed-forward neural networks, and are a generalization of both logistic regression and the perceptron. Despite the more complicated structures presented, we show that the key building blocks remain the same: the network is trained by minimizing a cost function. This minimization is implemented with backpropagation, which adapts the gradient descent algorithm introduced in the previous chapter to multilayer neural networks.
This chapter covers the perceptron, the simplest neural network architecture. In general, neural networks are machine learning architectures loosely inspired by the structure of biological brains. The perceptron is the simplest example of such architectures: it contains a single artificial neuron. The perceptron will form the building block for the more complicated architectures discussed later in the book. However, rather than starting directly with the discussion of this algorithm, we will start with something simpler: a children’s book and some fundamental observations about machine learning. From these, we will formalize our first machine learning algorithm, the perceptron.
In this chapter, we provide an implementation of the multilayer neural network described in Chapter 5, along with several of the best practices discussed in Chapter 6. Still keeping things fairly simple, our network will consist of two fully connected layers: a hidden layer and an output layer. Between these layers, we will include dropout and a nonlinearity. Further, we make use of two PyTorch classes: a Dataset and a DataLoader. The advantage of using these classes is that they make several things easy, including data shuffling and batching. Last, since the classifier’s architecture has become more complex, for optimization we transition from stochastic gradient descent to the Adam optimizer to take advantage of its additional features such as momentum and L2 regularization.
This chapter motivates the need for a book that covers both theoretical and practical aspects of deep learning for natural language processing. We summarize the content of the book, as well as aspects that are not within scope, and current limitations of deep learning in general.
In Chapters 10 and 12, we focused on two common usages of recurrent neural networks and transformer networks: acceptors and transducers. In this chapter, we discuss a third architecture for both recurrent neural networks and transformer networks: encoder-decoder methods. We introduce three encoder-decoder architectures, which enable important NLP applications such as machine translation. In particular, we discuss the sequence-to-sequence method of Sutskever et al. (2014), which couples an encoder long short-term memory with a decoder long short-term memory. We follow this method with the approach of Bahdanau et al. (2015), which extends the previous decoder with an attention component, which produces a different encoding of the source text for each decoded word. Last, we introduce the complete encoder-decoder transformer network, which relies on three attention mechanisms: one within the encoder (which we discussed in Chapter 12), a similar one that operates over decoded words, and, importantly, an attention component that connects the input words with the decoded ones.
As mentioned in Chapter 8, the distributional similarity algorithms discussed there conflate all senses of a word into a single numerical representation (or embedding). For example, the word bank receives a single representation, regardless of its financial (e.g., as in the bank gives out loans) or geological (e.g., bank of the river) sense. This chapter introduces a solution for this limitation in the form of a new neural architecture called transformer networks, which learns contextualized embeddings of words, which, as the name indicates, change depending on the context in which the words appear. That is, the word bank receives a different numerical representation for each of its instances in the two texts above because the contexts in which they occur are different. We also discuss several architectural choices that enabled the tremendous success of transformer networks: self attention, multiple heads, stacking of multiple layers, and subword tokenization, as well as how transformers can be pretrained on large amounts of data through through masked language modeling and next-sentence prediction.
Up to this point, we have only discussed neural approaches for text classification (e.g., review and news classification) that handle the text as a bag of words. That is, we aggregate the words either by representing them as explicit features in a feature vector or by averaging their numerical representations (i.e., embeddings). Although this strategy completely ignores the order in which words occur in a sentence, it has been repeatedly shown to be a good solution for many practical natural language processing applications that are driven by text classification. Nevertheless, for many natural language processing tasks such as part-of-speech tagging, we need to capture the word-order information more explicitly. Sequence models capture exactly this scenario, where classification decisions must be made using not only the current information but also the context in which it appears. In particular, we discuss several types of recurrent neural networks, including stacked (or deep) recurrent neural networks, bidirectional recurrent neural networks, and long short-term memory networks. Last, we introduced conditional random fields, which extend recurrent neural networks with an extra layer that explicitly models transition probabilities between two cells.
Deep Learning is becoming increasingly important in a technology-dominated world. However, the building of computational models that accurately represent linguistic structures is complex, as it involves an in-depth knowledge of neural networks, and the understanding of advanced mathematical concepts such as calculus and statistics. This book makes these complexities accessible to those from a humanities and social sciences background, by providing a clear introduction to deep learning for natural language processing. It covers both theoretical and practical aspects, and assumes minimal knowledge of machine learning, explaining the theory behind natural language in an easy-to-read way. It includes pseudo code for the simpler algorithms discussed, and actual Python code for the more complicated architectures, using modern deep learning libraries such as PyTorch and Hugging Face. Providing the necessary theoretical foundation and practical tools, this book will enable readers to immediately begin building real-world, practical natural language processing systems.
Coreference resolution is the task of identifying and clustering mentions that refer to the same entity in a document. Based on state-of-the-art deep learning approaches, end-to-end coreference resolution considers all spans as candidate mentions and tackles mention detection and coreference resolution simultaneously. Recently, researchers have attempted to incorporate document-level context using higher-order inference (HOI) to improve end-to-end coreference resolution. However, HOI methods have been shown to have marginal or even negative impact on coreference resolution. In this paper, we reveal the reasons for the negative impact of HOI coreference resolution. Contextualized representations (e.g., those produced by BERT) for building span embeddings have been shown to be highly anisotropic. We show that HOI actually increases and thus worsens the anisotropy of span embeddings and makes it difficult to distinguish between related but distinct entities (e.g., pilots and flight attendants). Instead of using HOI, we propose two methods, Less-Anisotropic Internal Representations (LAIR) and Data Augmentation with Document Synthesis and Mention Swap (DSMS), to learn less-anisotropic span embeddings for coreference resolution. LAIR uses a linear aggregation of the first layer and the topmost layer of contextualized embeddings. DSMS generates more diversified examples of related but distinct entities by synthesizing documents and by mention swapping. Our experiments show that less-anisotropic span embeddings improve the performance significantly (+2.8 F1 gain on the OntoNotes benchmark) reaching new state-of-the-art performance on the GAP dataset.
Here we present an improved approach for automated annotation of New Testament corpora with cross-lingual semantic concordance based on Strong’s numbers. Based on already annotated texts, they provide references to the original Greek words. Since scientific editions and translations of biblical texts are often not available for scientific purposes and are rarely freely available, there is a lack of up-to-date training data. In addition, since annotation, curation, and quality control of alignments between these texts are expensive, there is a lack of available biblical resources for scholars. We present two improved approaches to the problem, based on dictionaries and already annotated biblical texts. We provide a detailed evaluation of annotated and unannotated translations. We also discuss a proof of concept based on English and German New Testament translations. The results presented in this paper are novel and, to our knowledge, unique. They show promising performance, although further research is needed.
Recent work on text simplification has focused on the use of control tokens to further the state-of-the-art. However, it is not easy to further improve without an in-depth comprehension of the mechanisms underlying control tokens. One unexplored factor is the tokenization strategy, which we also explore. In this paper, we (1) reimplemented AudienCe-CEntric Sentence Simplification, (2) explored the effects and interactions of varying control tokens, (3) tested the influences of different tokenization strategies, (4) demonstrated how separate control tokens affect performance and (5) proposed new methods to predict the value of control tokens. We show variations of performance in the four control tokens separately. We also uncover how the design of control tokens could influence performance and give some suggestions for designing control tokens. We show the newly proposed method with higher performance in both SARI (a common scoring metric in text simplificaiton) and BERTScore (a score derived from the BERT language model) and potential in real applications.
Usage of large language models and chat bots will almost surely continue to grow, since they are so easy to use, and so (incredibly) credible. I would be more comfortable with this reality if we encouraged more evaluations with humans-in-the-loop to come up with a better characterization of when the machine can be trusted and when humans should intervene. This article will describe a homework assignment, where I asked my students to use tools such as chat bots and web search to write a number of essays. Even after considerable discussion in class on hallucinations, many of the essays were full of misinformation that should have been fact-checked. Apparently, it is easier to believe ChatGPT than to be skeptical. Fact-checking and web search are too much trouble.
Specialised pre-trained language models are becoming more frequent in Natural language Processing (NLP) since they can potentially outperform models trained on generic texts. BioBERT (Sanh et al., Distilbert, a distilled version of bert: smaller, faster, cheaper and lighter. arXiv preprint arXiv: 1910.01108, 2019) and BioClinicalBERT (Alsentzer et al., Publicly available clinical bert embeddings. In Proceedings of the 2nd Clinical Natural Language Processing Workshop, pp. 72–78, 2019) are two examples of such models that have shown promise in medical NLP tasks. Many of these models are overparametrised and resource-intensive, but thanks to techniques like knowledge distillation, it is possible to create smaller versions that perform almost as well as their larger counterparts. In this work, we specifically focus on development of compact language models for processing clinical texts (i.e. progress notes, discharge summaries, etc). We developed a number of efficient lightweight clinical transformers using knowledge distillation and continual learning, with the number of parameters ranging from $15$ million to $65$ million. These models performed comparably to larger models such as BioBERT and ClinicalBioBERT and significantly outperformed other compact models trained on general or biomedical data. Our extensive evaluation was done across several standard datasets and covered a wide range of clinical text-mining tasks, including natural language inference, relation extraction, named entity recognition and sequence classification. To our knowledge, this is the first comprehensive study specifically focused on creating efficient and compact transformers for clinical NLP tasks. The models and code used in this study can be found on our Huggingface profile at https://huggingface.co/nlpie and Github page at https://github.com/nlpie-research/Lightweight-Clinical-Transformers, respectively, promoting reproducibility of our results.
Automatic dialog systems have become a mainstream part of online customer service. Many such systems are built, maintained, and improved by customer service specialists, rather than dialog systems engineers and computer programmers. As conversations between people and machines become commonplace, it is critical to understand what is working, what is not, and what actions can be taken to reduce the frequency of inappropriate system responses. These analyses and recommendations need to be presented in terms that directly reflect the user experience rather than the internal dialog processing.
This paper introduces and explains the use of Actionable Conversational Quality Indicators (ACQIs), which are used both to recognize parts of dialogs that can be improved and to recommend how to improve them. This combines benefits of previous approaches, some of which have focused on producing dialog quality scoring while others have sought to categorize the types of errors the dialog system is making. We demonstrate the effectiveness of using ACQIs on LivePerson internal dialog systems used in commercial customer service applications and on the publicly available LEGOv2 conversational dataset. We report on the annotation and analysis of conversational datasets showing which ACQIs are important to fix in various situations.
The annotated datasets are then used to build a predictive model which uses a turn-based vector embedding of the message texts and achieves a 79% weighted average f1-measure at the task of finding the correct ACQI for a given conversation. We predict that if such a model worked perfectly, the range of potential improvement actions a bot-builder must consider at each turn could be reduced by an average of 81%.