Word order difference between source and target languages is a major obstacle to cross-lingual transfer, especially in the dependency parsing task. Current works are mostly based on order-agnostic models or word reordering to mitigate this problem. However, such methods either do not leverage grammatical information naturally contained in word order or are computationally expensive as the permutation space grows exponentially with the sentence length. Moreover, the reordered source sentence with an unnatural word order may be a form of noising that harms the model learning. To this end, we propose an Implicit Word Reordering framework with Knowledge Distillation (IWR-KD). This framework is inspired by that deep networks are good at learning feature linearization corresponding to meaningful data transformation, e.g. word reordering. To realize this idea, we introduce a knowledge distillation framework composed of a word-reordering teacher model and a dependency parsing student model. We verify our proposed method on Universal Dependency Treebanks across 31 different languages and show it outperforms a series of competitors, together with experimental analysis to illustrate how our method works towards training a robust parser.

Cross-lingual learning aims to transfer knowledge from one natural language to another. Zero-shot cross-lingual named entity recognition (NER) tasks are to train an NER model on source languages and to identify named entities in other languages. Existing knowledge distillation-based models in a teacher-student manner leverage the unlabeled samples from the target languages and show their superiority in this setting. However, the valuable similarity information between tokens in the target language is ignored. And the teacher model trained solely on the source language generates low-quality pseudo-labels. These two facts impact the performance of cross-lingual NER. To improve the reliability of the teacher model, in this study, we first introduce one extra simple binary classification teacher model by similarity learning to measure if the inputs are from the same class. We note that this binary classification auxiliary task is easier, and the two teachers simultaneously supervise the student model for better performance. Furthermore, given such a stronger student model, we propose a progressive knowledge distillation framework that extensively fine-tunes the teacher model on the target-language pseudo-labels generated by the student model. Empirical studies on three datasets across seven different languages show that our presented model outperforms state-of-the-art methods.

Cross-lingual named entity recognition task is one of the critical problems for evaluating the potential transfer learning techniques on low resource languages.Knowledge distillation using pre-trained multilingual language models between source and target languages have shown their superiority in transfer.However, existing cross-lingual distillation models merely consider the potential transferability between two identical single tasks across both domains.Other possible auxiliary tasks to improve the learning performance have not been fully investigated.In this study, based on the knowledge distillation framework and multitask learning, we introduce the similarity metric model as an auxiliary task to improve the cross-lingual NER performance on the target domain.Specifically, an entity recognizer and a similarity evaluator are first trained in parallel as two teachers from the source domain.Then, two tasks in the student model are supervised by these teachers simultaneously.Empirical studies on the three datasets across 7 different languages confirm the effectiveness of the proposed model.