基于元学习的少样本增量知识图谱链接预测
Meta-Learning Based Few-Shot Link Prediction for Emerging Knowledge Graph
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摘要:研究背景 知识图谱以语义三元组的形式把海量结构化、半结构化、非结构化信息表示为客观世界可认知的知识库,具有强大的语义表达、存储能力。尽管知识图谱中常常包含了大量知识条目,但其一般仍是不完整的且亟待补充的。为了解决这一问题,知识图谱的链接预测任务被提出,旨在对图谱中缺失的三元组进行预测,从而对整张图谱进行补全。近年来,基于神经网络的知识图谱表示学习方法已经在图谱链接预测任务上取得了不错的成绩。目的 现实世界中知识图谱并不是静态不变的,而是动态增长的。传统的知识图谱链接预测方法往往忽略了这一点,他们要求图谱中的实体与关系必须在训练时出现过,否则无法获得实体与关系对应的特征表示,因而无法在预测阶段对从未出现过的实体或关系进行预测。此外,当图谱中出现新增实体时,其相关联的图结构或语义信息往往较少,只能提供少量学习样本,这也极大限制了现有方法的表示能力。因此,我们希望提出一种新的知识图谱链接预测方法,可以适用于增量场景下少样本的知识图谱链接预测,使得图谱能更好的适用于现实应用场景。方法 本文设计了一种基于元学习的知识图谱表示学习方法,从全图抽取高阶语义特征来对增量场景下的新增实体进行表示,在图神经网络中引入记忆单元存储路径的语义信息,并利用元学习的方法在训练过程中模拟少样本进行训练,使得模型可以完成少样本下增量知识图谱的链接预测任务。结果 本文在由公开数据集FB15k-237与NELL-995所构建出的增量图谱数据集上对所提出的模型与所有基线进行比较,实验证明模型效果超过了所有对比基线,评价指标MRR在两个数据集上分别达到了0.397与0.291。消融实验证明了我们所提出的图特征传递模型和全局语义特征的有效性。此外,我们对模型的损失收敛效率以及训练和测试的效率均进行了研究与分析。结论 针对少样本下的增量知识图谱链接预测问题,本文提出了一种基于元学习的知识图谱表示学习方法,在图神经网络中引入记忆单元,抽取了图谱中的全局语义信息,并利用元学习框架模拟了少样本场景进行模型训练。实验证明该模型在少样本的条件下依旧可以在增量图谱的链接预测任务上取得不错的效果,且其在样本数充足时仍然适用。该方法可以帮助图谱更好的适用到现实应用场景中,例如可以帮助解决推荐系统冷启动问题,多轮对话的话题切换问题等等。Abstract: Inductive knowledge graph embedding (KGE) aims to embed unseen entities in emerging knowledge graphs (KGs). The major recent studies of inductive KGE embed unseen entities by aggregating information from their neighboring entities and relations with graph neural networks (GNNs). However, these methods rely on the existing neighbors of unseen entities and suffer from two common problems: data sparsity and feature smoothing. Firstly, the data sparsity problem means unseen entities usually emerge with few triplets containing insufficient information. Secondly, the effectiveness of the features extracted from original KGs will degrade when repeatedly propagating these features to represent unseen entities in emerging KGs, which is termed feature smoothing problem. To tackle the two problems, we propose a novel model entitled Meta-Learning Based Memory Graph Convolutional Network (MMGCN) consisting of three different components: 1) the two-layer information transforming module (TITM) developed to effectively transform information from original KGs to emerging KGs; 2) the hyper-relation feature initializing module (HFIM) proposed to extract type-level features shared between KGs and obtain a coarse-grained representation for each entity with these features; and 3) the meta-learning training module (MTM) designed to simulate the few-shot emerging KGs and train the model in a meta-learning framework. The extensive experiments conducted on the few-shot link prediction task for emerging KGs demonstrate the superiority of our proposed model MMGCN compared with state-of-the-art methods.