DOCSLIB.ORG

Psdvec: a Toolbox for Incremental and Scalable Word Embedding

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Psdvec: a Toolbox for Incremental and Scalable Word Embedding Neurocomputing ∎ (∎∎∎∎) ∎∎∎–∎∎∎ Contents lists available at ScienceDirect Neurocomputing journal homepage: www.elsevier.com/locate/neucom PSDVec: A toolbox for incremental and scalable word embedding Shaohua Li a,n, Jun Zhu b, Chunyan Miao a a Joint NTU-UBC Research Centre of Excellence in Active Living for the Elderly (LILY), Nanyang Technological University, Singapore b Tsinghua University, PR China article info abstract Article history: PSDVec is a Python/Perl toolbox that learns word embeddings, i.e. the mapping of words in a natural Received 28 July 2015 language to continuous vectors which encode the semantic/syntactic regularities between the words. Received in revised form PSDVec implements a word embedding learning method based on a weighted low-rank positive semi- 28 January 2016 definite approximation. To scale up the learning process, we implement a blockwise online learning Accepted 25 May 2016 algorithm to learn the embeddings incrementally. This strategy greatly reduces the learning time of word Communicated by Wang Gang embeddings on a large vocabulary, and can learn the embeddings of new words without re-learning the whole vocabulary. On 9 word similarity/analogy benchmark sets and 2 Natural Language Processing Keywords: (NLP) tasks, PSDVec produces embeddings that has the best average performance among popular word Word embedding embedding tools. PSDVec provides a new option for NLP practitioners. Matrix factorization & 2016 Elsevier B.V. All rights reserved. Incremental learning 1. Introduction methods use two different sets of embeddings for words and their context words, respectively. SVD based optimization procedures Word embedding has gained popularity as an important un- are used to yield two singular matrices. Only the left singular supervised Natural Language Processing (NLP) technique in recent matrix is used as the embeddings of words. However, SVD oper- years. The task of word embedding is to derive a set of vectors in a ates on G⊤G, which incurs information loss in G, and may not Euclidean space corresponding to words which best fit certain correctly capture the signed correlations between words. An em- statistics derived from a corpus. These vectors, commonly referred pirical comparison of popular methods is presented in [5]. to as the embeddings, capture the semantic/syntactic regularities The toolbox presented in this paper is an implementation of between the words. Word embeddings can supersede the tradi- our previous work [8]. It is a new MF-based method, but is based tional one-hot encoding of words as the input of an NLP learning on eigendecomposition instead. This toolbox is based on [8], system, and can often significantly improve the performance of where we establish a Bayesian generative model of word embed- the system. ding, derive a weighted low-rank positive semidefinite approx- There are two lines of word embedding methods. The first line imation problem to the Pointwise Mutual Information (PMI) ma- is neural word embedding models, which use softmax regression trix, and finally solve it using eigendecomposition. Eigende- to fit bigram probabilities and are optimized with Stochastic composition avoids the information loss in based methods, and 1 Gradient Descent (SGD). One of the best known tools is word2vec the yielded embeddings are of higher quality than SVD-based [10]. The second line is low-rank matrix factorization (MF)-based methods. However eigendecomposition is known to be difficult to methods, which aim to reconstruct certain bigram statistics matrix scale up. To make our method scalable to large vocabularies, we extracted from a corpus, by the product of two low rank factor exploit the sparsity pattern of the weight matrix and implement a 2 matrices. Representative methods/toolboxes include Hyperwords divide-and-conquer approximate solver to find the embeddings 3 4 5 [4,5], GloVe [11], Singular [14], and Sparse [2]. All these incrementally. Our toolbox is named Positive-Semidefinite Vectors (PSDVec). It n Corresponding author. offers the following advantages over other word embedding tools: E-mail addresses: [email protected] (S. Li), [email protected] (J. Zhu), [email protected] (C. Miao). 1. The incremental solver in PSDVec has a time complexity 1 https://code.google.com/p/word2vec/ O (cd2 n) and space complexity O (cd), where n is the number of 2 https://bitbucket.org/omerlevy/hyperwords words in a vocabulary, d is the specified dimensionality of em- 3 http://nlp.stanford.edu/projects/glove/ 4 fi https://github.com/karlstratos/singular beddings, and cn⪡ is the number of speci ed core words. Note 5 https://github.com/mfaruqui/sparse-coding that the space complexity does not increase with the http://dx.doi.org/10.1016/j.neucom.2016.05.093 0925-2312/& 2016 Elsevier B.V. All rights reserved. Please cite this article as: S. Li, et al., PSDVec: A toolbox for incremental and scalable word embedding, Neurocomputing (2016), http: //dx.doi.org/10.1016/j.neucom.2016.05.093i 2 S. Li et al. / Neurocomputing ∎ (∎∎∎∎) ∎∎∎–∎∎∎ vocabulary. In contrast, other MF-based solvers, including the difficult to scale up. As a remedy, we implement an approximate core embedding generation are of O (n3) time complexity and solution that learns embeddings incrementally. The incremental O (n2) space complexity.6 Hence asymptotically, PSDVec takes learning proceeds as follows: about O(cd2/n2) of the time and O(cd/n2) of the space of other MF-based solvers. 1. Partition the vocabulary S into K consecutive groups S1,,… Sk. 2. Given the embeddings of an original vocabulary, PSDVec is able Take K¼3 as an example. S1 consists of the most frequent to learn the embeddings of new words incrementally. To our words, referred to as the core words, and the remaining words best knowledge, none of other word embedding tools provide are noncore words. this functionality; instead, new words have to be learned to- 2. Accordingly partition G into K Â K blocks as gether with old words in batch mode. A common situation is ⎛ GGG⎞ that we have a huge general corpus such as English Wikipedia, ⎜ 11 12 13⎟ ⎜ GGG⎟. and also have a small domain-specific corpus, such as the NIPS ⎜ 21 22 23⎟ dataset. In the general corpus, specific terms may appear rarely. ⎝ GGG31 32 33⎠ It would be desirable to train the embeddings of a general vo- Partition f (H) in the same way. GH, f () correspond to core– cabulary on the general corpus, and then incrementally learn 11 11 core bigrams (consisting of two core words). Partition V into words that are unique in the domain-specific corpus. Then this feature of incremental learning could come into play. ⎛ ⎞ ⎜ ⎟ 3. On word similarity/analogy benchmark sets and common Nat- ⎜ VVV123⎟. ⎝ ⎠ ural Language Processing (NLP) tasks, PSDVec produces em- ⏟S1 ⏟SS23⏟ beddings that has the best average performance among popular ⊤ 3. For core words, set μ = 0, and solve arg min ||GVV11 −1 1 ||f (H ) word embedding tools. i V ⁎ 1 using eigendecomposition, obtaining core embeddings V1 . 4. PSDVec is established as a Bayesian generative model [8]. The ⁎ ⁎ 4. Set V = V ,andfind V that minimizes the total penalty of the 12th probabilistic modeling endows PSDVec clear probabilistic inter- 1 1 2 and 21th blocks (the 22th block is ignored due to its high sparsity): pretation, and the modular structure of the generative model is ⊤ 2 ⊤ 2 2 easy to customize and extend in a principled manner. For arg min‖−‖+‖−‖+GVV12 1 2 ff()HH12 GVV21 2 1 () 21 ∑ μi ‖‖ vsi . V example, global factors like topics can be naturally incorporated, 2 si∈S2 resulting in a hybrid model [9] of word embedding and Latent The columns in V are independent, thus for each v ,itisaseparate Dirichlet Allocation [1]. For such extensions, PSDVec would 2 si weighted ridge regression problem, which has a closed-form serve as a good prototype. While in other methods, the regres- solution. sion objectives are usually heuristic, and other factors are ⁎ 5. For any other set of noncore words S , find V that minimizes difficult to be incorporated. k k the total penalty of the 1kth and k1th blocks, ignoring all other kjth and jkth blocks. ⁎ 6. Combine all subsets of embeddings to form V . Here 2. Problem and solution ⁎ ⁎⁎⁎ V =(VVV123,,). PSDVec implements a low-rank MF-based word embedding Pss()ij, method. This method aims to fit the PMI()=ssij , log using Ps()()ij Ps 3. Software architecture and functionalities v⊤ v , where and Ps( , s) are the empirical unigram and bi- sj si Ps( i ) ij Our toolbox consists of 4 Python/Perl scripts: extractwiki. gram probabilities, respectively, and vsi is the embedding of si. The regression residuals PMIss , vv⊤ are penalized by a mono- py, gramcount.pl, factorize.py and evaluate.py. Fig. 1 ()−ij sj si presents the overall architecture. tonic transformation f (·) of Ps( ij, s), which implies that, for more frequent (therefore more important) bigram si, sj, we expect it is extractwiki.py fi better fitted. The optimization objective in the matrix form is 1. rst receives a Wikipedia snapshot as input; it then removes non-textual elements, non-English words and W ⁎ ⊤ 2 VGVVv=||−||+‖‖arg minf ()H ∑ μi si 2 , V i=1 ()1 where G is the PMI matrix, V is the embedding matrix, H is the bigram probabilities matrix, ||·||f (H) is the f ()−H weighted Frobe- nius-norm, and μi are the Tikhonov regularization coefficients. The purpose of the Tikhonov regularization is to penalize overlong embeddings. The overlength of embeddings is a sign of overfitting the corpus. Our experiments showed that, with such regulariza- tion, the yielded embeddings perform better on all tasks. Eq. (1) is to find a weighted low-rank positive semidefinite approximation to G. Prior to computing G, the bigram probabilities {Ps()}ij, s are smoothed using Jelinek–Mercer Smoothing.
Load more

Recommended publications
  • Evaluation of Machine Learning Algorithms for Sms Spam Filtering
    EVALUATION OF MACHINE LEARNING ALGORITHMS FOR SMS SPAM FILTERING David Bäckman Bachelor Thesis, 15 credits Bachelor Of Science Programme in Computing Science 2019 Abstract The purpose of this thesis is to evaluate dierent machine learning algorithms and methods for text representation in order to determine what is best suited to use to distinguish between spam SMS and legitimate SMS. A data set that contains 5573 real SMS has been used to train the algorithms K-Nearest Neighbor, Support Vector Machine, Naive Bayes and Logistic Regression. The dierent methods that have been used to represent text are Bag of Words, Bigram and Word2Vec. In particular, it has been investigated if semantic text representations can improve the performance of classication. A total of 12 combinations have been evaluated with help of the metrics accuracy and F1-score. The results shows that Logistic Regression together with Bag of Words reach the highest accuracy and F1-score. Bigram as text representation seems to work worse then the others methods. Word2Vec can increase the performnce for K- Nearst Neigbor but not for the other algorithms. Acknowledgements I would like to thank my supervisor Kai-Florian Richter for all good advice and guidance through the project. I would also like to thank all my classmates for help and support during the education, you have made it possible for me to reach this day. Contents 1 Introduction 1 1.1 Background1 1.2 Purpose and Research Questions1 2 Related Work 3 3 Theoretical Background 5 3.1 The Choice of Algorithms5 3.2 Classication
    [Show full text]
  • NLP - Assignment 2
    NLP - Assignment 2 Week 2 December 27th, 2016 1. A 5-gram model is a order Markov Model: (a) Six (b) Five (c) Four (d) Constant Ans : c) Four 2. For the following corpus C1 of 3 sentences, what is the total count of unique bi- grams for which the likelihood will be estimated? Assume we do not perform any pre-processing, and we are using the corpus as given. (i) ice cream tastes better than any other food (ii) ice cream is generally served after the meal (iii) many of us have happy childhood memories linked to ice cream (a) 22 (b) 27 (c) 30 (d) 34 Ans : b) 27 3. Arrange the words \curry, oil and tea" in descending order, based on the frequency of their occurrence in the Google Books n-grams. The Google Books n-gram viewer is available at https://books.google.com/ngrams: (a) tea, oil, curry (c) curry, tea, oil (b) curry, oil, tea (d) oil, tea, curry Ans: d) oil, tea, curry 4. Given a corpus C2, The Maximum Likelihood Estimation (MLE) for the bigram \ice cream" is 0.4 and the count of occurrence of the word \ice" is 310. The likelihood of \ice cream" after applying add-one smoothing is 0:025, for the same corpus C2. What is the vocabulary size of C2: 1 (a) 4390 (b) 4690 (c) 5270 (d) 5550 Ans: b)4690 The Questions from 5 to 10 require you to analyse the data given in the corpus C3, using a programming language of your choice.
    [Show full text]
  • 3 Dictionaries and Tolerant Retrieval
    Online edition (c)2009 Cambridge UP DRAFT! © April 1, 2009 Cambridge University Press. Feedback welcome. 49 Dictionaries and tolerant 3 retrieval In Chapters 1 and 2 we developed the ideas underlying inverted indexes for handling Boolean and proximity queries. Here, we develop techniques that are robust to typographical errors in the query, as well as alternative spellings. In Section 3.1 we develop data structures that help the search for terms in the vocabulary in an inverted index. In Section 3.2 we study WILDCARD QUERY the idea of a wildcard query: a query such as *a*e*i*o*u*, which seeks doc- uments containing any term that includes all the five vowels in sequence. The * symbol indicates any (possibly empty) string of characters. Users pose such queries to a search engine when they are uncertain about how to spell a query term, or seek documents containing variants of a query term; for in- stance, the query automat* would seek documents containing any of the terms automatic, automation and automated. We then turn to other forms of imprecisely posed queries, focusing on spelling errors in Section 3.3. Users make spelling errors either by accident, or because the term they are searching for (e.g., Herman) has no unambiguous spelling in the collection. We detail a number of techniques for correcting spelling errors in queries, one term at a time as well as for an entire string of query terms. Finally, in Section 3.4 we study a method for seeking vo- cabulary terms that are phonetically close to the query term(s).
    [Show full text]
  • N-Gram-Based Machine Translation
    N-gram-based Machine Translation ∗ JoseB.Mari´ no˜ ∗ Rafael E. Banchs ∗ Josep M. Crego ∗ Adria` de Gispert ∗ Patrik Lambert ∗ Jose´ A. R. Fonollosa ∗ Marta R. Costa-jussa` Universitat Politecnica` de Catalunya This article describes in detail an n-gram approach to statistical machine translation. This ap- proach consists of a log-linear combination of a translation model based on n-grams of bilingual units, which are referred to as tuples, along with four specific feature functions. Translation performance, which happens to be in the state of the art, is demonstrated with Spanish-to-English and English-to-Spanish translations of the European Parliament Plenary Sessions (EPPS). 1. Introduction The beginnings of statistical machine translation (SMT) can be traced back to the early fifties, closely related to the ideas from which information theory arose (Shannon and Weaver 1949) and inspired by works on cryptography (Shannon 1949, 1951) during World War II. According to this view, machine translation was conceived as the problem of finding a sentence by decoding a given “encrypted” version of it (Weaver 1955). Although the idea seemed very feasible, enthusiasm faded shortly afterward because of the computational limitations of the time (Hutchins 1986). Finally, during the nineties, two factors made it possible for SMT to become an actual and practical technology: first, significant increment in both the computational power and storage capacity of computers, and second, the availability of large volumes of bilingual data. The first SMT systems were developed in the early nineties (Brown et al. 1990, 1993). These systems were based on the so-called noisy channel approach, which models the probability of a target language sentence T given a source language sentence S as the product of a translation-model probability p(S|T), which accounts for adequacy of trans- lation contents, times a target language probability p(T), which accounts for fluency of target constructions.
    [Show full text]
  • Title and Link Description Improving Distributional Similarity With
    title and link description Improving Distributional Similarity • word similarity with Lessons Learned from Word ... • analogy • qualitativ: compare neighborhoods across Dependency-Based Word Embeddings embeddings • word similarity • word similarity Multi-Granularity Chinese Word • analogy Embedding • qualitative: local neighborhoods A Mixture Model for Learning Multi- • word similarity Sense Word Embeddings • analogy Learning Crosslingual Word • multilingual Embeddings without Bilingual Corpora • word similarities (monolingual) Word Embeddings with Limited • word similarity Memory • phrase similarity A Latent Variable Model Approach to • analogy PMI-based Word Embeddings Prepositional Phrase Attachment over • extrinsic Word Embedding Products A Simple Word Embedding Model for • lexical substitution (nearest Lexical Substitution neighbors after vector averaging) Segmentation-Free Word Embedding • extrinsic for Unsegmented Languages • word similarity Evaluation methods for unsupervised • analogy word embeddings • concept categorization • selectional preference Dict2vec : Learning Word Embeddings • word similarity using Lexical Dictionaries • extrinsic Task-Oriented Learning of Word • extrinsic Embeddings for Semantic Relation ... Refining Word Embeddings for • extrinsic Sentiment Analysis Language classification from bilingual • word similarity word embedding graphs Learning principled bilingual mappings • multilingual of word embeddings while ... A Word Embedding Approach to • extrinsic Identifying Verb-Noun Idiomatic ... Deep Multilingual
    [Show full text]
  • Arxiv:2006.14799V2 [Cs.CL] 18 May 2021 the Same User Input
    Evaluation of Text Generation: A Survey Evaluation of Text Generation: A Survey Asli Celikyilmaz [email protected] Facebook AI Research Elizabeth Clark [email protected] University of Washington Jianfeng Gao [email protected] Microsoft Research Abstract The paper surveys evaluation methods of natural language generation (NLG) systems that have been developed in the last few years. We group NLG evaluation methods into three categories: (1) human-centric evaluation metrics, (2) automatic metrics that require no training, and (3) machine-learned metrics. For each category, we discuss the progress that has been made and the challenges still being faced, with a focus on the evaluation of recently proposed NLG tasks and neural NLG models. We then present two examples for task-specific NLG evaluations for automatic text summarization and long text generation, and conclude the paper by proposing future research directions.1 1. Introduction Natural language generation (NLG), a sub-field of natural language processing (NLP), deals with building software systems that can produce coherent and readable text (Reiter & Dale, 2000a) NLG is commonly considered a general term which encompasses a wide range of tasks that take a form of input (e.g., a structured input like a dataset or a table, a natural language prompt or even an image) and output a sequence of text that is coherent and understandable by humans. Hence, the field of NLG can be applied to a broad range of NLP tasks, such as generating responses to user questions in a chatbot, translating a sentence or a document from one language into another, offering suggestions to help write a story, or generating summaries of time-intensive data analysis.
    [Show full text]
  • Word Senses and Wordnet Lady Bracknell
    Speech and Language Processing. Daniel Jurafsky & James H. Martin. Copyright © 2021. All rights reserved. Draft of September 21, 2021. CHAPTER 18 Word Senses and WordNet Lady Bracknell. Are your parents living? Jack. I have lost both my parents. Lady Bracknell. To lose one parent, Mr. Worthing, may be regarded as a misfortune; to lose both looks like carelessness. Oscar Wilde, The Importance of Being Earnest ambiguous Words are ambiguous: the same word can be used to mean different things. In Chapter 6 we saw that the word “mouse” has (at least) two meanings: (1) a small rodent, or (2) a hand-operated device to control a cursor. The word “bank” can mean: (1) a financial institution or (2) a sloping mound. In the quote above from his play The Importance of Being Earnest, Oscar Wilde plays with two meanings of “lose” (to misplace an object, and to suffer the death of a close person). We say that the words ‘mouse’ or ‘bank’ are polysemous (from Greek ‘having word sense many senses’, poly- ‘many’ + sema, ‘sign, mark’).1 A sense (or word sense) is a discrete representation of one aspect of the meaning of a word. In this chapter WordNet we discuss word senses in more detail and introduce WordNet, a large online the- saurus —a database that represents word senses—with versions in many languages. WordNet also represents relations between senses. For example, there is an IS-A relation between dog and mammal (a dog is a kind of mammal) and a part-whole relation between engine and car (an engine is a part of a car).
    [Show full text]
  • A Unigram Orientation Model for Statistical Machine Translation
    A Unigram Orientation Model for Statistical Machine Translation Christoph Tillmann IBM T.J. Watson Research Center Yorktown Heights, NY 10598 [email protected] Abstract b5 airspace In this paper, we present a unigram segmen- b4 tation model for statistical machine transla- Lebanese b tion where the segmentation units are blocks: 3 pairs of phrases without internal structure. The violate b2 segmentation model uses a novel orientation warplanes component to handle swapping of neighbor b1 blocks. During training, we collect block un- Israeli igram counts with orientation: we count how A A A t A A A often a block occurs to the left or to the right of l l l n l l l some predecessor block. The orientation model T H A t m j l is shown to improve translation performance A r s h j w b } over two models: 1) no block re-ordering is b r k A y n r y A l A used, and 2) the block swapping is controlled A P } n only by a language model. We show exper- t y y imental results on a standard Arabic-English l y translation task. P 1 Introduction Figure 1: An Arabic-English block translation example taken from the devtest set. The Arabic words are roman- In recent years, phrase-based systems for statistical ma- ized. chine translation (Och et al., 1999; Koehn et al., 2003; Venugopal et al., 2003) have delivered state-of-the-art performance on standard translation tasks. In this pa- section 3, block swapping where only a trigram language per, we present a phrase-based unigram system similar model is used to compute probabilities between neighbor to the one in (Tillmann and Xia, 2003), which is ex- blocks fails to improve translation performance.
    [Show full text]
  • Heafield, K. and A. Lavie. "Voting on N-Grams for Machine Translation
    Voting on N-grams for Machine Translation System Combination Kenneth Heafield and Alon Lavie Language Technologies Institute Carnegie Mellon University 5000 Forbes Avenue Pittsburgh, PA 15213 fheafield,[email protected] Abstract by a single weight and further current features only guide decisions at the word level. To remedy this System combination exploits differences be- situation, we propose new features that account for tween machine translation systems to form a multiword behavior, each with a separate set of sys- combined translation from several system out- tem weights. puts. Core to this process are features that reward n-gram matches between a candidate 2 Features combination and each system output. Systems differ in performance at the n-gram level de- Most combination schemes generate many hypothe- spite similar overall scores. We therefore ad- sis combinations, score them using a battery of fea- vocate a new feature formulation: for each tures, and search for a hypothesis with highest score system and each small n, a feature counts to output. Formally, the system generates hypoth- n-gram matches between the system and can- esis h, evaluates feature function f, and multiplies didate. We show post-evaluation improvement of 6.67 BLEU over the best system on NIST linear weight vector λ by feature vector f(h) to ob- T MT09 Arabic-English test data. Compared to tain score λ f(h). The score is used to rank fi- a baseline system combination scheme from nal hypotheses and to prune partial hypotheses dur- WMT 2009, we show improvement in the ing beam search. The beams contain hypotheses of range of 1 BLEU point.
    [Show full text]
  • Part I Word Vectors I: Introduction, Svd and Word2vec 2 Natural Language in Order to Perform Some Task
    CS224n: Natural Language Processing with Deep 1 Learning 1 Course Instructors: Christopher Lecture Notes: Part I Manning, Richard Socher 2 Word Vectors I: Introduction, SVD and Word2Vec 2 Authors: Francois Chaubard, Michael Fang, Guillaume Genthial, Rohit Winter 2019 Mundra, Richard Socher Keyphrases: Natural Language Processing. Word Vectors. Singu- lar Value Decomposition. Skip-gram. Continuous Bag of Words (CBOW). Negative Sampling. Hierarchical Softmax. Word2Vec. This set of notes begins by introducing the concept of Natural Language Processing (NLP) and the problems NLP faces today. We then move forward to discuss the concept of representing words as numeric vectors. Lastly, we discuss popular approaches to designing word vectors. 1 Introduction to Natural Language Processing We begin with a general discussion of what is NLP. 1.1 What is so special about NLP? What’s so special about human (natural) language? Human language is a system specifically constructed to convey meaning, and is not produced by a physical manifestation of any kind. In that way, it is very different from vision or any other machine learning task. Natural language is a dis- Most words are just symbols for an extra-linguistic entity : the crete/symbolic/categorical system word is a signifier that maps to a signified (idea or thing). For instance, the word "rocket" refers to the concept of a rocket, and by extension can designate an instance of a rocket. There are some exceptions, when we use words and letters for expressive sig- naling, like in "Whooompaa". On top of this, the symbols of language can be encoded in several modalities : voice, gesture, writing, etc that are transmitted via continuous signals to the brain, which itself appears to encode things in a continuous manner.
    [Show full text]
  • Phrase Based Language Model for Statistical Machine Translation
    Phrase Based Language Model for Statistical Machine Translation Technical Report by Chen, Geliang 1 Abstract Reordering is a challenge to machine translation (MT) systems. In MT, the widely used approach is to apply word based language model (LM) which considers the constituent units of a sentence as words. In speech recognition (SR), some phrase based LM have been proposed. However, those LMs are not necessarily suitable or optimal for reordering. We propose two phrase based LMs which considers the constituent units of a sentence as phrases. Experiments show that our phrase based LMs outperform the word based LM with the respect of perplexity and n-best list re-ranking. Key words: machine translation, language model, phrase based This version of report is identical to the dissertation approved from Yuanpei Institute of Peking University to receive the Bachelor Degree of Probability and Statistics by Chen, Geliang. Advisor: Assistant Professor Dr.rer.nat. Jia Xu Evaluation Date: 20. June. 2013 2 Contents Abstract .......................................................................................................................... 2 Contents …………………………………………………………………………………………………………………..3 1 Introduction ................................................................................................................. 4 2 Review of the Word Based LM ................................................................................... 5 2.1 Sentence probability ............................................................................................
    [Show full text]
  • Phrase-Based Attentions
    Under review as a conference paper at ICLR 2019 PHRASE-BASED ATTENTIONS Phi Xuan Nguyen, Shafiq Joty Nanyang Technological University, Singapore [email protected], [email protected] ABSTRACT Most state-of-the-art neural machine translation systems, despite being different in architectural skeletons (e.g., recurrence, convolutional), share an indispensable feature: the Attention. However, most existing attention methods are token-based and ignore the importance of phrasal alignments, the key ingredient for the suc- cess of phrase-based statistical machine translation. In this paper, we propose novel phrase-based attention methods to model n-grams of tokens as attention entities. We incorporate our phrase-based attentions into the recently proposed Transformer network, and demonstrate that our approach yields improvements of 1.3 BLEU for English-to-German and 0.5 BLEU for German-to-English transla- tion tasks on WMT newstest2014 using WMT’16 training data. 1 INTRODUCTION Neural Machine Translation (NMT) has established breakthroughs in many different translation tasks, and has quickly become the standard approach to machine translation. NMT offers a sim- ple encoder-decoder architecture that is trained end-to-end. Most NMT models (except a few like (Kaiser & Bengio, 2016) and (Huang et al., 2018)) possess attention mechanisms to perform align- ments of the target tokens to the source tokens. The attention module plays a role analogous to the word alignment model in Statistical Machine Translation or SMT (Koehn, 2010). In fact, the trans- former network introduced recently by Vaswani et al. (2017) achieves state-of-the-art performance in both speed and BLEU scores (Papineni et al., 2002) by using only attention modules.
    [Show full text]