eNeMILP: Non-Monotonic Incremental Language Processing

自然语言处理(NLP)的研究正在推动许多应用程序的进步，如搜索引擎和个人数字助理，如苹果的Siri和亚马逊的Alexa。在许多自然语言处理任务中，要预测的输出是代表句子的图形，例如句法分析中的句法树或语义分析中的意义表示。此外，在自然语言生成和机器翻译等其他任务中，预测的输出是文本，即单词序列。增量建模方法成功地解决了这两种类型的自然语言处理任务，其中预测被分解为构造输出的一系列动作。尽管增量建模取得了成功，但增量建模的一个基本限制是，被考虑的动作通常单调地构造输出，例如在自然语言生成中，每个动作向输出中添加一个词，但从不移除或改变先前预测的词。因此，完全依赖单调动作可能会降低准确性，因为不正确动作的效果无法修正。此外，这些动作将被用来预测以下可能导致误差级联的动作。我们提出了一个为期18个月的项目来解决这一限制，并学习非单调增量语言处理模型，即考虑可以取消先前预测的结果的动作的增量模型。加入非单调动作的挑战是，与它们的单调动作不同，它们不能直接从通常可用于训练的标记数据中推断，因此使得标准的监督学习方法不适用。为了解决这个问题，我们将在模拟学习范式下开发新的算法来学习非单调增量模型，而不假设操作级监督，而是依赖实例级损失函数和模型自己的预测，以便学习如何从错误的操作中恢复以避免错误级联。为了实现这一目标，该建议有以下研究目标：1)以一种通用的方式对结构化输出的非单调增量预测进行建模，以适用于以自然语言文本为输出的各种任务。2)利用模仿学习学习非单调增量预测因子，并在BLEU等自动测量和人工评价方面改进单调增量预测模型的准确性。3)将所提出的方法扩展到以图形为输出的结构化预测任务。4)发布所提出方法的软件实现，以促进可重复性和更广泛地被研究界采用。所提出的研究集中于增量语言处理模型的基本限制，这些模型已成功地应用于各种自然语言处理任务，因此我们预计该建议将具有广泛的学术影响。此外，我们将对其进行评估的任务，即自然语言生成和语义分析，是自然语言界面和个人数字助理的重要组成部分。改进这些技术将使人们更容易获得数字信息和服务。我们将通过与我们的项目合作伙伴亚马逊的合作来展示我们方法的好处，亚马逊不仅在云计算积分方面支持该提议，还将主办研究助理，以便将该项目的结果应用于行业规模的数据集。

Research in natural language processing (NLP) is driving advances in many applications such as search engines and personal digital assistants, e.g. Apple's Siri and Amazon's Alexa. In many NLP tasks the output to be predicted is a graph representing the sentence, e.g. a syntax tree in syntactic parsing or a meaning representation in semantic parsing. Furthermore, in other tasks such as natural language generation and machine translation the predicted output is text, i.e. a sequence of words. Both types of NLP tasks have been tackled successfully with incremental modelling approaches in which prediction is decomposed into a sequence of actions constructing the output.Despite its success, a fundamental limitation in incremental modelling is that the actions considered typically construct the output monotonically, e.g. in natural language generation each action adds a word to the output but never removes or changes a previously predicted one. Thus, relying exclusively on monotonic actions can decrease accuracy, since the effect of incorrect actions cannot be amended. Furthermore, these actions will be used to predict the following ones, likely to result in an error cascade.We propose an 18-month project to address this limitation and learn non-monotonic incremental language processing models, i.e. incremental models that consider actions that can "undo" the outcome of previously predicted ones. The challenge in incorporating non-monotonic actions is that, unlike their monotonic counterparts, they are not straightforward to infer from the labelled data typically available for training, thus rendering standard supervised learning approaches inapplicable. To overcome this issue we will develop novel algorithms under the imitation learning paradigm to learn non-monotonic incremental models without assuming action-level supervision, relying instead on instance-level loss functions and the model's own predictions in order to learn how to recover from incorrect actions to avoid error cascades. To succeed in this goal, this proposal has the following research objectives:1) To model non-monotonic incremental prediction of structured outputs in a generic way that can be applied to a variety of tasks with natural language text as output2) To learn non-monotonic incremental predictors using imitation learning and improve upon the accuracy of monotonic incremental models both in terms of automatic measures such as BLEU and human evaluation. 3) To extend the proposed approach to structured prediction tasks with graph as output.4) To release software implementations of the proposed methods to facilitate reproducibility and wider adoption by the research community.The research proposed focuses on a fundamental limitation in incremental language processing models, which have been successfully applied to a variety of natural language processing tasks, thus we anticipate the proposal to have a wide academic impact. Furthermore, the tasks we will evaluate it on, namely natural language generation and semantic parsing, are essential components to natural language interfaces and personal digital assistants. Improving these technologies will enhance accessibility to digital information and services. We will demonstrate the benefits of our approach through our collaboration with our project partners Amazon who are supporting the proposal both in terms of cloud computing credits but also by hosting the research associate in order to apply the outcomes of the project to industry-scale datasets.