HeGang Chen


2024

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Hierarchical Topic Modeling via Contrastive Learning and Hyperbolic Embedding
Zhicheng Lin | HeGang Chen | Yuyin Lu | Yanghui Rao | Hao Xu | Hanjiang Lai
Proceedings of the 2024 Joint International Conference on Computational Linguistics, Language Resources and Evaluation (LREC-COLING 2024)

Hierarchical topic modeling, which can mine implicit semantics in the corpus and automatically construct topic hierarchical relationships, has received considerable attention recently. However, the current hierarchical topic models are mainly based on Euclidean space, which cannot well retain the implicit hierarchical semantic information in the corpus, leading to irrational structure of the generated topics. On the other hand, the existing Generative Adversarial Network (GAN) based neural topic models perform satisfactorily, but they remain constrained by pattern collapse due to the discontinuity of latent space. To solve the above problems, with the hypothesis of hyperbolic space, we propose a novel GAN-based hierarchical topic model to mine high-quality topics by introducing contrastive learning to capture information from documents. Furthermore, the distinct tree-like property of hyperbolic space preserves the implicit hierarchical semantics of documents in topic embeddings, which are projected into the hyperbolic space. Finally, we use a multi-head self-attention mechanism to learn implicit hierarchical semantics of topics and mine topic structure information. Experiments on real-world corpora demonstrate the remarkable performance of our model on topic coherence and topic diversity, as well as the rationality of the topic hierarchy.

2023

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Nonlinear Structural Equation Model Guided Gaussian Mixture Hierarchical Topic Modeling
HeGang Chen | Pengbo Mao | Yuyin Lu | Yanghui Rao
Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)

Hierarchical topic models, which can extract semantically meaningful topics from a textcorpus in an unsupervised manner and automatically organise them into a topic hierarchy, have been widely used to discover the underlying semantic structure of documents. However, the existing models often assume in the prior that the topic hierarchy is a tree structure, ignoring symmetrical dependenciesbetween topics at the same level. Moreover, the sparsity of text data often complicate the analysis. To address these issues, we propose NSEM-GMHTM as a deep topic model, witha Gaussian mixture prior distribution to improve the model’s ability to adapt to sparse data, which explicitly models hierarchical and symmetric relations between topics through the dependency matrices and nonlinear structural equations. Experiments on widely used datasets show that our NSEM-GMHTM generates more coherent topics and a more rational topic structure when compared to state-of-theart baselines. Our code is available at https: //github.com/nbnbhwyy/NSEM-GMHTM.

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Graph-based Relation Mining for Context-free Out-of-vocabulary Word Embedding Learning
Ziran Liang | Yuyin Lu | HeGang Chen | Yanghui Rao
Proceedings of the 61st Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers)

The out-of-vocabulary (OOV) words are difficult to represent while critical to the performance of embedding-based downstream models. Prior OOV word embedding learning methods failed to model complex word formation well. In this paper, we propose a novel graph-based relation mining method, namely GRM, for OOV word embedding learning. We first build a Word Relationship Graph (WRG) based on word formation and associate OOV words with their semantically relevant words, which can mine the relational information inside word structures. Subsequently, our GRM can infer high-quality embeddings for OOV words through passing and aggregating semantic attributes and relational information in the WRG, regardless of contextual richness. Extensive experiments demonstrate that our model significantly outperforms state-of-the-art baselines on both intrinsic and downstream tasks when faced with OOV words.