I am currently a postdoctoral Research Associate in the Knowledge Representation and Reasoning (KRR) group at the Department of Computer Science, University of Oxford.
My research interests revolve around Natural Language Processing, Knowledge Engineering, and Deep Learning, currently with the following specific topics:
",
which does not match the baseurl
("
") configured in _config.yml
.
baseurl
in _config.yml
to "
".
Yuan He, Zhangdie Yuan, Jiaoyan Chen, Ian Horrocks
NeurIPS 2024
TL;DR: We introduce a novel approach to re-train transformer encoder-based language models as Hierarchy Transformer encoders (HiTs), leveraging the expansive nature of hyperbolic psace.
Abstract: Interpreting hierarchical structures latent in language is a key limitation of current language models (LMs). While previous research has implicitly leveraged these hierarchies to enhance LMs, approaches for their explicit encoding are yet to be explored. To address this, we introduce a novel approach to re-train transformer encoder-based LMs as Hierarchy Transformer encoders (HiTs), harnessing the expansive nature of hyperbolic space. Our method situates the output embedding space of pre-trained LMs within a Poincaré ball with a curvature that adapts to the embedding dimension, followed by training on hyperbolic clustering and centripetal losses. These losses are designed to effectively cluster related entities (input as texts) and organise them hierarchically. We evaluate HiTs against pre-trained LMs, standard fine-tuned LMs, and several hyperbolic embedding baselines, focusing on their capabilities in simulating transitive inference, predicting subsumptions, and transferring knowledge across hierarchies. The results demonstrate that HiTs consistently outperform all baselines in these tasks, underscoring the effectiveness and transferability of our re-trained hierarchy encoders.
Yuan He
University of Oxford (PhD Thesis) 2024
TL;DR: My PhD Thesis.
Abstract: Ontology, originally a philosophical term, refers to the study of being and existence. The concept was introduced to Artificial Intelligence (AI) as a knowledge-based system that can model and share knowledge about entities and their relationships in a machine-readable format. Ontologies offer a structured and logical formalism of human knowledge, enabling expressive representations and reliable reasoning within defined domains. Meanwhile, modern deep learning-based language models (LMs) represent a significant milestone in the field of Natural Language Processing (NLP), as they incorporate substantial background knowledge from the vast and complex distribution of textual data. This thesis explores the synergy between these two paradigms, focusing primarily on the use of LMs in ontology engineering and, more broadly, in knowledge engineering. The goal is to automate or semi-automate the process of ontology construction and curation. Ontology engineering includes a wide array of tasks within the life cycle of ontology development. This thesis concentrates on three key aspects: (i) ontology alignment, which seeks to align equivalent concepts across different ontologies to achieve data integration; (ii) ontology completion, which focuses on filling in missing subsumption relationships between ontology concepts; and (iii) hierarchy embedding, which aims to develop versatile and interpretable neural representations for hierarchical structures derived not only from ontologies but also applicable to other forms of hierarchical data. These representations can facilitate a broad spectrum of downstream ontology engineering tasks, such as (i) and (ii), and are adaptable for more general applications in hierarchy-aware contexts. This thesis is organised into three parts. The first part establishes the foundations necessary for understanding ontologies and LMs. The chapter on ontologies initiates with a basic overview of computational ontologies, then provides an introduction of the description logic formalisms that underpin them. It concludes with the formal definitions of the three ontology engineering tasks this thesis focuses on. Transitioning to LMs, the subsequent chapter begins with a chronological overview of their evolution, followed by detailed exposition of various typical LMs along this evolution. The discussion then proceeds to contemporary transformer-based LMs, elaborating on their architecture and different learning paradigms they adopt. The chapter concludes with a review of how LMs and knowledge bases (including ontologies) interact and influence each other, highlighting the mutual benefits of this integration for both fields of study. With the comprehensive background provided in the first part, the second part of the thesis delves into specific methodologies that have been developed. This part comprises three chapters, each corresponding to the application of LMs in ontology alignment, ontology completion, and hierarchy embedding, respectively. In the chapter on LMs for ontology alignment, we introduce BERTMap, a novel pipeline system that employs LM fine-tuning for improved alignment prediction and ontology semantics for alignment refinement. We will also mention the Bio-ML track of the Ontology Alignment Evaluation Initiative (OAEI), which has emerged as a benchmarking platform for a variety of ontology alignment systems over the past two years. The chapter on LMs for ontology completion presents OntoLAMA, a collection of LM probing datasets and a prompt-based LM probing approach that effectively predicts subsumptions, even with limited training resources. Lastly, the section on LMs for hierarchy embedding discusses the re-training of LMs as Hierarchy Transformer encoders (HiT), addressing the limitations of LMs in explicitly interpreting and encoding hierarchies, including those extracted from ontologies. The third part of the thesis details the practical implementations. We mainly present DeepOnto, a Python package designed for ontology engineering utilising deep learning, with an emphasis on LMs. DeepOnto offers a range of basic to advanced ontology processing functionalities to support deep learning-based ontology engineering development. This package also includes polished implementations of our systems and resources mentioned in Part II. In summary, this thesis advocates for a more holistic approach in AI development, where the integration of LMs and ontologies can lead to a more advanced, explainable, and useful paradigm in knowledge engineering and beyond.
Zifeng Ding, Yifeng Li, Yuan He, Antonio Norelli, Jingcheng Wu, Volker Tresp, Yunpu Ma, Michael Bronstein.
Arxiv 2024
TL;DR: We introduce DyGMamba, a model that utilizes state space models (SSMs) for continuous-time dynamic graph (CTDG) representation learning.
Abstract: Learning useful representations for continuous-time dynamic graphs (CTDGs) is challenging, due to the concurrent need to span long node interaction histories and grasp nuanced temporal details. In particular, two problems emerge: (1) Encoding longer histories requires more computational resources, making it crucial for CTDG models to maintain low computational complexity to ensure efficiency; (2) Meanwhile, more powerful models are needed to identify and select the most critical temporal information within the extended context provided by longer histories. To address these problems, we propose a CTDG representation learning model named DyGMamba, originating from the popular Mamba state space model (SSM). DyGMamba first leverages a node-level SSM to encode the sequence of historical node interactions. Another time-level SSM is then employed to exploit the temporal patterns hidden in the historical graph, where its output is used to dynamically select the critical information from the interaction history. We validate DyGMamba experimentally on the dynamic link prediction task. The results show that our model achieves state-of-the-art in most cases. DyGMamba also maintains high efficiency in terms of computational resources, making it possible to capture long temporal dependencies with a limited computation budget.
Yuan He, Jiaoyan Chen, Hang Dong, Ian Horrocks, Carlo Allocca, Taehun Kim, Brahmananda Sapkota
Semantic Web 2024
TL;DR: A Python package for ontology engineering with deep learning and language models.
Abstract: Integrating deep learning techniques, particularly language models (LMs), with knowledge representation techniques like ontologies has raised widespread attention, urging the need of a platform that supports both paradigms. Although packages such as OWL API and Jena offer robust support for basic ontology processing features, they lack the capability to transform various types of information within ontologies into formats suitable for downstream deep learning-based applications. Moreover, widely-used ontology APIs are primarily Java-based while deep learning frameworks like PyTorch and Tensorflow are mainly for Python programming. To address the needs, we present DeepOnto, a Python package designed for ontology engineering with deep learning. The package encompasses a core ontology processing module founded on the widely-recognised and reliable OWL API, encapsulating its fundamental features in a more "Pythonic" manner and extending its capabilities to incorporate other essential components including reasoning, verbalisation, normalisation, taxonomy, projection, and more. Building on this module, DeepOnto offers a suite of tools, resources, and algorithms that support various ontology engineering tasks, such as ontology alignment and completion, by harnessing deep learning methods, primarily pre-trained LMs. In this paper, we also demonstrate the practical utility of DeepOnto through two use-cases: the Digital Health Coaching in Samsung Research UK and the Bio-ML track of the Ontology Alignment Evaluation Initiative (OAEI).
Yuan He, Jiaoyan Chen, Ernesto Jiménez-Ruiz, Hang Dong, Ian Horrocks
ACL (Findings) 2023
TL;DR: Probing the conceptual (ontological) knowledge in pre-trained language models.
Abstract: Investigating whether pre-trained language models (LMs) can function as knowledge bases (KBs) has raised wide research interests recently. However, existing works focus on simple, triple-based, relational KBs, but omit more sophisticated, logic-based, conceptualised KBs such as OWL ontologies. To investigate an LM's knowledge of ontologies, we propose OntoLAMA, a set of inference-based probing tasks and datasets from ontology subsumption axioms involving both atomic and complex concepts. We conduct extensive experiments on ontologies of different domains and scales, and our results demonstrate that LMs encode relatively less background knowledge of Subsumption Inference (SI) than traditional Natural Language Inference (NLI) but can improve on SI significantly when a small number of samples are given. We will open-source our code and datasets.
Yuan He, Jiaoyan Chen, Denvar Antonyrajah, Ian Horrocks
AAAI 2022
TL;DR: We introduce BERTMap, a pipeline ontology alignment system that leverages textual information from input ontologies to fine-tune BERT for lexical matching, structural and logical information to further refine the output mappings.
Abstract: Ontology alignment (a.k.a ontology matching (OM)) plays a critical role in knowledge integration. Owing to the success of machine learning in many domains, it has been applied in OM. However, the existing methods, which often adopt ad-hoc feature engineering or non-contextual word embeddings, have not yet outperformed rule-based systems especially in an unsupervised setting. In this paper, we propose a novel OM system named BERTMap which can support both unsupervised and semi-supervised settings. It first predicts mappings using a classifier based on fine-tuning the contextual embedding model BERT on text semantics corpora extracted from ontologies, and then refines the mappings through extension and repair by utilizing the ontology structure and logic. Our evaluation with three alignment tasks on biomedical ontologies demonstrates that BERTMap can often perform better than the leading OM systems LogMap and AML.