Relation Extraction (RE) has been extended to cross-document scenarios because many relations are not simply described in a single document. This inevitably brings the challenge of efficient open-space evidence retrieval to support the inference of cross-document relations, along with the challenge of multi-hop reasoning on top of entities and evidence scattered in an open set of documents. To combat these challenges, we propose Mr.CoD, a multi-hop evidence retrieval method based on evidence path mining and ranking with adapted dense retrievers. We explore multiple variants of retrievers to show evidence retrieval is an essential part in cross-document RE. Experiments on CodRED show that evidence retrieval with Mr.Cod effectively acquires cross-document evidence that essentially supports open-setting cross-document RE. Additionally, we show that Mr.CoD facilitates evidence retrieval and boosts end-to-end RE performance with effective multi-hop reasoning in both closed and open settings of RE.

Machine reading comprehension (MRC) is a long-standing topic in natural language processing (NLP). The MRC task aims to answer a question based on the given context. Recently studies focus on multi-hop MRC which is a more challenging extension of MRC, which to answer a question some disjoint pieces of information across the context are required. Due to the complexity and importance of multi-hop MRC, a large number of studies have been focused on this topic in recent years, therefore, it is necessary and worth reviewing the related literature. This study aims to investigate recent advances in the multi-hop MRC approaches based on 31 studies from 2018 to 2022. In this regard, first, the multi-hop MRC problem definition will be introduced, then 31 models will be reviewed in detail with a strong focus on their multi-hop aspects. They also will be categorized based on their main techniques. Finally, a fine-grain comprehensive comparison of the models and techniques will be presented.

多跳的推理（即跨两个或多个文档的推理）是NLP模型的关键要素，该模型利用大型语料库表现出广泛的知识。为了检索证据段落，多跳模型必须与整个啤酒花的快速增长的搜索空间抗衡，代表结合多个信息需求的复杂查询，并解决有关在训练段落之间跳出的最佳顺序的歧义。我们通过Baleen解决了这些问题，Baleen可以提高多跳检索的准确性，同时从多跳的训练信号中学习强大的训练信号的准确性。为了驯服搜索空间，我们提出了凝结的检索，该管道总结了每个跃点后检索到单个紧凑型上下文的管道。为了建模复杂的查询，我们引入了一个重点的后期相互作用检索器，该检索器允许同一查询表示的不同部分匹配不同的相关段落。最后，为了推断无序的训练段落中的跳跃依赖性，我们设计了潜在的跳跃订购，这是一种弱者的策略，在该策略中，受过训练的检索员本身选择了啤酒花的顺序。我们在检索中评估Baleen的两跳问答和多跳的要求验证，并确定最先进的绩效。

我们研究了检查问题的事实，旨在识别给定索赔的真实性。具体而言，我们专注于事实提取和验证（发烧）及其伴随数据集的任务。该任务包括从维基百科检索相关文件（和句子）并验证文件中的信息是否支持或驳斥所索赔的索赔。此任务至关重要，可以是假新闻检测和医疗索赔验证等应用程序块。在本文中，我们以通过以结构化和全面的方式呈现文献来更好地了解任务的挑战。我们通过分析不同方法的技术视角并讨论发热数据集的性能结果，描述了所提出的方法，这是最熟悉的和正式结构化的数据集，就是事实提取和验证任务。我们还迄今为止迄今为止确定句子检索组件的有益损失函数的最大实验研究。我们的分析表明，采样负句对于提高性能并降低计算复杂性很重要。最后，我们描述了开放的问题和未来的挑战，我们激励了未来的任务研究。

Open-domain question answering relies on efficient passage retrieval to select candidate contexts, where traditional sparse vector space models, such as TF-IDF or BM25, are the de facto method. In this work, we show that retrieval can be practically implemented using dense representations alone, where embeddings are learned from a small number of questions and passages by a simple dualencoder framework. When evaluated on a wide range of open-domain QA datasets, our dense retriever outperforms a strong Lucene-BM25 system greatly by 9%-19% absolute in terms of top-20 passage retrieval accuracy, and helps our end-to-end QA system establish new state-of-the-art on multiple open-domain QA benchmarks. 1 * Equal contribution 1 The code and trained models have been released at https://github.com/facebookresearch/DPR.

A key component of fact verification is thevevidence retrieval, often from multiple documents. Recent approaches use dense representations and condition the retrieval of each document on the previously retrieved ones. The latter step is performed over all the documents in the collection, requiring storing their dense representations in an index, thus incurring a high memory footprint. An alternative paradigm is retrieve-and-rerank, where documents are retrieved using methods such as BM25, their sentences are reranked, and further documents are retrieved conditioned on these sentences, reducing the memory requirements. However, such approaches can be brittle as they rely on heuristics and assume hyperlinks between documents. We propose a novel retrieve-and-rerank method for multi-hop retrieval, that consists of a retriever that jointly scores documents in the knowledge source and sentences from previously retrieved documents using an autoregressive formulation and is guided by a proof system based on natural logic that dynamically terminates the retrieval process if the evidence is deemed sufficient. This method is competitive with current state-of-the-art methods on FEVER, HoVer and FEVEROUS-S, while using $5$ to $10$ times less memory than competing systems. Evaluation on an adversarial dataset indicates improved stability of our approach compared to commonly deployed threshold-based methods. Finally, the proof system helps humans predict model decisions correctly more often than using the evidence alone.

知识密集型语言任务（苏格兰信）通常需要大量信息来提供正确的答案。解决此问题的一种流行范式是将搜索系统与机器读取器相结合，前者检索支持证据，后者检查它们以产生答案。最近，读者组成部分在大规模预培养的生成模型的帮助下见证了重大进展。同时，搜索组件中的大多数现有解决方案都依赖于传统的``索引 - retrieve-then-Rank''管道，该管道遭受了巨大的内存足迹和端到端优化的困难。受到最新构建基于模型的IR模型的努力的启发，我们建议用新颖的单步生成模型替换传统的多步搜索管道，该模型可以极大地简化搜索过程并以端到端的方式进行优化。我们表明，可以通过一组经过适当设计的预训练任务来学习强大的生成检索模型，并被采用以通过进一步的微调来改善各种下游苏格兰短裙任务。我们将预训练的生成检索模型命名为Copusbrain，因为有关该语料库的所有信息均以其参数进行编码，而无需构造其他索引。经验结果表明，在苏格兰语基准上的检索任务并建立了新的最新性能，Copusbrain可以极大地超过强大的基准。我们还表明，在零农源和低资源设置下，科体班运行良好。

Multi-hop machine reading comprehension is a challenging task in natural language processing, which requires more reasoning ability across multiple documents. Spectral models based on graph convolutional networks grant inferring abilities and lead to competitive results. However, part of them still faces the challenge of analyzing the reasoning in a human-understandable way. Inspired by the concept of the Grandmother Cells in cognitive neuroscience, a spatial graph attention framework named ClueReader was proposed in this paper, imitating the procedure. This model is designed to assemble the semantic features in multi-level representations and automatically concentrate or alleviate information for reasoning via the attention mechanism. The name ClueReader is a metaphor for the pattern of the model: regard the subjects of queries as the start points of clues, take the reasoning entities as bridge points, consider the latent candidate entities as the grandmother cells, and the clues end up in candidate entities. The proposed model allows us to visualize the reasoning graph, then analyze the importance of edges connecting two entities and the selectivity in the mention and candidate nodes, which can be easier to be comprehended empirically. The official evaluations in the open-domain multi-hop reading dataset WikiHop and the Drug-drug Interactions dataset MedHop prove the validity of our approach and show the probability of the application of the model in the molecular biology domain.

Multi-hop Machine reading comprehension is a challenging task with aim of answering a question based on disjoint pieces of information across the different passages. The evaluation metrics and datasets are a vital part of multi-hop MRC because it is not possible to train and evaluate models without them, also, the proposed challenges by datasets often are an important motivation for improving the existing models. Due to increasing attention to this field, it is necessary and worth reviewing them in detail. This study aims to present a comprehensive survey on recent advances in multi-hop MRC evaluation metrics and datasets. In this regard, first, the multi-hop MRC problem definition will be presented, then the evaluation metrics based on their multi-hop aspect will be investigated. Also, 15 multi-hop datasets have been reviewed in detail from 2017 to 2022, and a comprehensive analysis has been prepared at the end. Finally, open issues in this field have been discussed.

自动问题应答（QA）系统的目的是以时间有效的方式向用户查询提供答案。通常在数据库（或知识库）或通常被称为语料库的文件集合中找到答案。在过去的几十年里，收购知识的扩散，因此生物医学领域的新科学文章一直是指数增长。因此，即使对于领域专家，也难以跟踪域中的所有信息。随着商业搜索引擎的改进，用户可以在某些情况下键入其查询并获得最相关的一小组文档，以及在某些情况下从文档中的相关片段。但是，手动查找所需信息或答案可能仍然令人疑惑和耗时。这需要开发高效的QA系统，该系统旨在为用户提供精确和精确的答案提供了生物医学领域的自然语言问题。在本文中，我们介绍了用于开发普通域QA系统的基本方法，然后彻底调查生物医学QA系统的不同方面，包括使用结构化数据库和文本集合的基准数据集和几种提出的方​​法。我们还探讨了当前系统的局限性，并探索潜在的途径以获得进一步的进步。

文档级关系提取（DRE）旨在识别两个实体之间的关系。实体可以对应于超越句子边界的多个提升。以前很少有研究已经调查了提及集成，这可能是有问题的，因为库鲁弗提到对特定关系没有同样有贡献。此外，事先努力主要关注实体级的推理，而不是捕获实体对之间的全局相互作用。在本文中，我们提出了两种新颖的技术，上下文指导的集成和交互推理（CGM2IR），以改善DRE。而不是简单地应用平均池，而是利用上下文来指导在加权和方式中的经验提升的集成。另外，对实体对图的相互作用推理在实体对图上执行迭代算法，以模拟关系的相互依赖性。我们在三个广泛使用的基准数据集中评估我们的CGM2IR模型，即Docred，CDR和GDA。实验结果表明，我们的模型优于以前的最先进的模型。

Multi-hop Question Answering over Knowledge Graph~(KGQA) aims to find the answer entities that are multiple hops away from the topic entities mentioned in a natural language question on a large-scale Knowledge Graph (KG). To cope with the vast search space, existing work usually adopts a two-stage approach: it firstly retrieves a relatively small subgraph related to the question and then performs the reasoning on the subgraph to accurately find the answer entities. Although these two stages are highly related, previous work employs very different technical solutions for developing the retrieval and reasoning models, neglecting their relatedness in task essence. In this paper, we propose UniKGQA, a novel approach for multi-hop KGQA task, by unifying retrieval and reasoning in both model architecture and parameter learning. For model architecture, UniKGQA consists of a semantic matching module based on a pre-trained language model~(PLM) for question-relation semantic matching, and a matching information propagation module to propagate the matching information along the edges on KGs. For parameter learning, we design a shared pre-training task based on question-relation matching for both retrieval and reasoning models, and then propose retrieval- and reasoning-oriented fine-tuning strategies. Compared with previous studies, our approach is more unified, tightly relating the retrieval and reasoning stages. Extensive experiments on three benchmark datasets have demonstrated the effectiveness of our method on the multi-hop KGQA task. Our codes and data are publicly available at https://github.com/RUCAIBox/UniKGQA.

随着自动假新闻检测技术的快速发展，事实提取和验证（发烧）吸引了更多的关注。该任务旨在从数百万个开放域Wikipedia文件中提取最相关的事实证据，然后验证相应索赔的可信度。尽管已经为该任务提出了几种强大的模型，但他们取得了长足的进步，但我们认为他们无法利用多视图上下文信息，因此无法获得更好的性能。在本文中，我们建议整合多视图上下文信息（IMCI）进行事实提取和验证。对于每个证据句子，我们定义两种上下文，即文档内部上下文和文档间的上下文}。文档内上下文由文档标题和同一文档中的所有其他句子组成。文档间的上下文包括所有其他证据，这些证据可能来自不同的文档。然后，我们集成了多视图上下文信息，以编码证据句子以处理任务。我们对发烧1.0共享任务的实验结果表明，我们的IMCI框架在事实提取和验证方面取得了长足的进步，并以72.97％的胜利发烧得分达到了最先进的表现，在线上获得了75.84％的标签准确度盲测。我们还进行消融研究以检测多视图上下文信息的影响。我们的代码将在https://github.com/phoenixsecularbird/imci上发布。

排名模型是信息检索系统的主要组成部分。排名的几种方法是基于传统的机器学习算法，使用一组手工制作的功能。最近，研究人员在信息检索中利用了深度学习模型。这些模型的培训结束于结束，以提取来自RAW数据的特征来排序任务，因此它们克服了手工制作功能的局限性。已经提出了各种深度学习模型，每个模型都呈现了一组神经网络组件，以提取用于排名的特征。在本文中，我们在不同方面比较文献中提出的模型，以了解每个模型的主要贡献和限制。在我们对文献的讨论中，我们分析了有前途的神经元件，并提出了未来的研究方向。我们还显示文档检索和其他检索任务之间的类比，其中排名的项目是结构化文档，答案，图像和视频。

Researchers produce thousands of scholarly documents containing valuable technical knowledge. The community faces the laborious task of reading these documents to identify, extract, and synthesize information. To automate information gathering, document-level question answering (QA) offers a flexible framework where human-posed questions can be adapted to extract diverse knowledge. Finetuning QA systems requires access to labeled data (tuples of context, question and answer). However, data curation for document QA is uniquely challenging because the context (i.e. answer evidence passage) needs to be retrieved from potentially long, ill-formatted documents. Existing QA datasets sidestep this challenge by providing short, well-defined contexts that are unrealistic in real-world applications. We present a three-stage document QA approach: (1) text extraction from PDF; (2) evidence retrieval from extracted texts to form well-posed contexts; (3) QA to extract knowledge from contexts to return high-quality answers -- extractive, abstractive, or Boolean. Using QASPER for evaluation, our detect-retrieve-comprehend (DRC) system achieves a +7.19 improvement in Answer-F1 over existing baselines while delivering superior context selection. Our results demonstrate that DRC holds tremendous promise as a flexible framework for practical scientific document QA.

对于开放式域问题的密集检索已被证明通过在问题通道对的大型数据集上培训来实现令人印象深刻的性能。我们调查是否可以以自我监督的方式学习密集的检索，并有效地应用没有任何注释。我们观察到这种情况下的检索斗争的现有借用模型，并提出了一种设计用于检索的新预制方案：重复跨度检索。我们在文档中使用经常性跨度来创建用于对比学习的伪示例。由此产生的模型 - 蜘蛛 - 在广泛的ODQA数据集上没有任何示例，并且与BM25具有竞争力，具有强烈的稀疏基线。此外，蜘蛛通常优于DPR在其他数据集的问题上培训的DPR培训的强大基线。我们将蜘蛛与BM25结合的混合猎犬改进了所有数据集的组件，并且通常与域中DPR模型具有竞争力，这些模型培训数万例培训。

使用来自表格（TableQA）的信息回答自然语言问题是最近的兴趣。在许多应用程序中，表未孤立，但嵌入到非结构化文本中。通常，通过将其部分与表格单元格内容或非结构化文本跨度匹配，并从任一源中提取答案来最佳地回答问题。这导致了HybridQA数据集引入的TextableQA问题的新空间。现有的表格表示对基于变换器的阅读理解（RC）架构的适应性未通过单个系统解决两个表示的不同模式。培训此类系统因对遥远监督的需求而进一步挑战。为了降低认知负担，培训实例通常包括问题和答案，后者匹配多个表行和文本段。这导致嘈杂的多实例培训制度不仅涉及表的行，而且涵盖了链接文本的跨度。我们通过提出Mitqa来回应这些挑战，这是一个新的TextableQA系统，明确地模拟了表行选择和文本跨度选择的不同但密切相关的概率空间。与最近的基线相比，我们的实验表明了我们的方法的优越性。该方法目前在HybridQA排行榜的顶部，并进行了一个试验集，在以前公布的结果上实现了对em和f1的21％的绝对改善。

知识基础问题回答（KBQA）旨在通过知识库（KB）回答问题。早期研究主要集中于回答有关KB的简单问题，并取得了巨大的成功。但是，他们在复杂问题上的表现远非令人满意。因此，近年来，研究人员提出了许多新颖的方法，研究了回答复杂问题的挑战。在这项调查中，我们回顾了KBQA的最新进展，重点是解决复杂问题，这些问题通常包含多个主题，表达复合关系或涉及数值操作。详细说明，我们从介绍复杂的KBQA任务和相关背景开始。然后，我们描述用于复杂KBQA任务的基准数据集，并介绍这些数据集的构建过程。接下来，我们提出两个复杂KBQA方法的主流类别，即基于语义解析的方法（基于SP）的方法和基于信息检索的方法（基于IR）。具体而言，我们通过流程设计说明了他们的程序，并讨论了它们的主要差异和相似性。之后，我们总结了这两类方法在回答复杂问题时会遇到的挑战，并解释了现有工作中使用的高级解决方案和技术。最后，我们结论并讨论了与复杂的KBQA有关的几个有希望的方向，以进行未来的研究。

在本文中，我们提出了一个新的密集检索模型，该模型通过深度查询相互作用学习了各种文档表示。我们的模型使用一组生成的伪Queries编码每个文档，以获取查询信息的多视文档表示。它不仅具有较高的推理效率，例如《香草双编码模型》，而且还可以在文档编码中启用深度查询文档的交互，并提供多方面的表示形式，以更好地匹配不同的查询。几个基准的实验证明了所提出的方法的有效性，表现出色的双重编码基准。

大多数阅读理解的研究都集中在基于单个文档甚至单一段落的问题上回答问题。我们介绍了一个神经模型，该神经模型集成和理由依赖于文档中和跨多个文档中的信息传播。我们将其作为图表上的推理问题构图。提及实体是该图的节点，而边缘编码不同提及（例如，内部和跨文档的共同参考）之间的关系。图形卷积网络（GCN）应用于这些图形，并经过训练以执行多步电推理。我们的实体-GCN方法是可扩展的，紧凑的，它可以在答案数据集的多文件问题上获得最新的结果，Wikihop（Welbl等，2018）。