Nikolaos Aletras


2022

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LexGLUE A Benchmark Dataset for Legal Language Understanding in EnglishLexGLUE: A Benchmark Dataset for Legal Language Understanding in English
Ilias Chalkidis | Abhik Jana | Dirk Hartung | Michael Bommarito | Ion Androutsopoulos | Daniel Katz | Nikolaos Aletras
Proceedings of the 60th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)

Laws and their interpretations legal arguments and agreements are typically expressed in writing leading to the production of vast corpora of legal text Their analysis which is at the center of legal practice becomes increasingly elaborate as these collections grow in size Natural language understanding NLU technologies can be a valuable tool to support legal practitioners in these endeavors Their usefulness however largely depends on whether current state of the art models can generalize across various tasks in the legal domain To answer this currently open question we introduce the Legal General Language Understanding Evaluation LexGLUE benchmark a collection of datasets for evaluating model performance across a diverse set of legal NLU tasks in a standardized way We also provide an evaluation and analysis of several generic and legal oriented models demonstrating that the latter consistently offer performance improvements across multiple tasks

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Dynamically Refined Regularization for Improving Cross-corpora Hate Speech Detection
Tulika Bose | Nikolaos Aletras | Irina Illina | Dominique Fohr
Findings of the Association for Computational Linguistics: ACL 2022

Hate speech classifiers exhibit substantial performance degradation when evaluated on datasets different from the source. This is due to learning spurious correlations between words that are not necessarily relevant to hateful language, and hate speech labels from the training corpus. Previous work has attempted to mitigate this problem by regularizing specific terms from pre-defined static dictionaries. While this has been demonstrated to improve the generalizability of classifiers, the coverage of such methods is limited and the dictionaries require regular manual updates from human experts. In this paper, we propose to automatically identify and reduce spurious correlations using attribution methods with dynamic refinement of the list of terms that need to be regularized during training. Our approach is flexible and improves the cross-corpora performance over previous work independently and in combination with pre-defined dictionaries.

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Translation Error Detection as Rationale Extraction
Marina Fomicheva | Lucia Specia | Nikolaos Aletras
Findings of the Association for Computational Linguistics: ACL 2022

Recent Quality Estimation QE models based on multilingual pre trained representations have achieved very competitive results in predicting the overall quality of translated sentences However detecting specifically which translated words are incorrect is a more challenging task especially when dealing with limited amounts of training data We hypothesize that not unlike humans successful QE models rely on translation errors to predict overall sentence quality By exploring a set of feature attribution methods that assign relevance scores to the inputs to explain model predictions we study the behaviour of state of the art sentence level QE models and show that explanations i.e. rationales extracted from these models can indeed be used to detect translation errors We therefore i introduce a novel semi supervised method for word level QE and ii propose to use the QE task as a new benchmark for evaluating the plausibility of feature attribution i.e. how interpretable model explanations are to humans

2021

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Improving the Faithfulness of Attention-based Explanations with Task-specific Information for Text Classification
George Chrysostomou | Nikolaos Aletras
Proceedings of the 59th Annual Meeting of the Association for Computational Linguistics and the 11th International Joint Conference on Natural Language Processing (Volume 1: Long Papers)

Neural network architectures in natural language processing often use attention mechanisms to produce probability distributions over input token representations. Attention has empirically been demonstrated to improve performance in various tasks, while its weights have been extensively used as explanations for model predictions. Recent studies (Jain and Wallace, 2019 ; Serrano and Smith, 2019 ; Wiegreffe and Pinter, 2019) have showed that it can not generally be considered as a faithful explanation (Jacovi and Goldberg, 2020) across encoders and tasks. In this paper, we seek to improve the faithfulness of attention-based explanations for text classification. We achieve this by proposing a new family of Task-Scaling (TaSc) mechanisms that learn task-specific non-contextualised information to scale the original attention weights. Evaluation tests for explanation faithfulness, show that the three proposed variants of TaSc improve attention-based explanations across two attention mechanisms, five encoders and five text classification datasets without sacrificing predictive performance. Finally, we demonstrate that TaSc consistently provides more faithful attention-based explanations compared to three widely-used interpretability techniques.

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Frustratingly Simple Pretraining Alternatives to Masked Language Modeling
Atsuki Yamaguchi | George Chrysostomou | Katerina Margatina | Nikolaos Aletras
Proceedings of the 2021 Conference on Empirical Methods in Natural Language Processing

Masked language modeling (MLM), a self-supervised pretraining objective, is widely used in natural language processing for learning text representations. MLM trains a model to predict a random sample of input tokens that have been replaced by a [ MASK ] placeholder in a multi-class setting over the entire vocabulary. When pretraining, it is common to use alongside MLM other auxiliary objectives on the token or sequence level to improve downstream performance (e.g. next sentence prediction). However, no previous work so far has attempted in examining whether other simpler linguistically intuitive or not objectives can be used standalone as main pretraining objectives. In this paper, we explore five simple pretraining objectives based on token-level classification tasks as replacements of MLM. Empirical results on GLUE and SQUAD show that our proposed methods achieve comparable or better performance to MLM using a BERT-BASE architecture. We further validate our methods using smaller models, showing that pretraining a model with 41 % of the BERT-BASE’s parameters, BERT-MEDIUM results in only a 1 % drop in GLUE scores with our best objective.

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Proceedings of the Natural Legal Language Processing Workshop 2021
Nikolaos Aletras | Ion Androutsopoulos | Leslie Barrett | Catalina Goanta | Daniel Preotiuc-Pietro
Proceedings of the Natural Legal Language Processing Workshop 2021

2019

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Journalist-in-the-Loop : Continuous Learning as a Service for Rumour Analysis
Twin Karmakharm | Nikolaos Aletras | Kalina Bontcheva
Proceedings of the 2019 Conference on Empirical Methods in Natural Language Processing and the 9th International Joint Conference on Natural Language Processing (EMNLP-IJCNLP): System Demonstrations

Automatically identifying rumours in social media and assessing their veracity is an important task with downstream applications in journalism. A significant challenge is how to keep rumour analysis tools up-to-date as new information becomes available for particular rumours that spread in a social network. This paper presents a novel open-source web-based rumour analysis tool that can continuous learn from journalists. The system features a rumour annotation service that allows journalists to easily provide feedback for a given social media post through a web-based interface. The feedback allows the system to improve an underlying state-of-the-art neural network-based rumour classification model. The system can be easily integrated as a service into existing tools and platforms used by journalists using a REST API.

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Proceedings of the Natural Legal Language Processing Workshop 2019
Nikolaos Aletras | Elliott Ash | Leslie Barrett | Daniel Chen | Adam Meyers | Daniel Preotiuc-Pietro | David Rosenberg | Amanda Stent
Proceedings of the Natural Legal Language Processing Workshop 2019

2017

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Multimodal Topic Labelling
Ionut Sorodoc | Jey Han Lau | Nikolaos Aletras | Timothy Baldwin
Proceedings of the 15th Conference of the European Chapter of the Association for Computational Linguistics: Volume 2, Short Papers

Topics generated by topic models are typically presented as a list of topic terms. Automatic topic labelling is the task of generating a succinct label that summarises the theme or subject of a topic, with the intention of reducing the cognitive load of end-users when interpreting these topics. Traditionally, topic label systems focus on a single label modality, e.g. textual labels. In this work we propose a multimodal approach to topic labelling using a simple feedforward neural network. Given a topic and a candidate image or textual label, our method automatically generates a rating for the label, relative to the topic. Experiments show that this multimodal approach outperforms single-modality topic labelling systems.