Author name cluster

Long Xia

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4 papers

1 author row

AAAI Conference 2026 Conference Paper

Beyond ReAct: A Planner-Centric Framework for Complex Tool-Augmented LLM Reasoning

Xiaolong Wei
Yuehu Dong
Xingliang Wang
Xingyu Zhang
Zhejun Zhao
Dongdong Shen
Long Xia
Dawei Yin

Existing tool-augmented large language models (LLMs) encounter significant challenges when processing complex queries. Current frameworks such as ReAct are prone to local optimization traps due to their reliance on incremental decision-making processes. To address these limitations, we propose a novel Planner-centric Plan-Execute paradigm that fundamentally resolves local optimization bottlenecks through architectural innovation. Central to our approach is a novel Planner model that performs global Directed Acyclic Graph (DAG) planning for complex queries, enabling optimized execution beyond conventional tool coordination. We also introduce ComplexTool-Plan, a large-scale benchmark dataset featuring complex queries that demand sophisticated multi-tool composition and coordination capabilities. Additionally, we develop a two-stage training methodology that integrates Supervised Fine-Tuning (SFT) with Group Relative Policy Optimization (GRPO), systematically enhancing the Planner's tool selection accuracy and global planning awareness through structured DAG-based planning. When integrated with a capable executor, our framework achieves state-of-the-art performance on the StableToolBench benchmark for complex user queries, demonstrating superior end-to-end execution capabilities and robust handling of intricate multi-tool workflows.

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TIST Journal 2025 Journal Article

Open Spatio-Temporal Foundation Models for Traffic Prediction

Zhonghang Li
Long Xia
Lei Shi
Yong Xu
Dawei Yin
Chao Huang

Accurate traffic forecasting is crucial for effective urban planning and transportation management, enabling efficient resource allocation and enhanced travel experiences. However, existing models often face limitations in generalization, struggling with zero-shot prediction on unseen regions and cities, as well as diminished long-term accuracy. This is primarily due to the inherent challenges in handling the spatial and temporal heterogeneity of traffic data, coupled with the significant distribution shift across time and space. In this work, we aim to unlock new possibilities for building versatile, resilient and adaptive spatio-temporal foundation models for traffic prediction. We introduce OpenCity, a foundation model that captures underlying spatio-temporal patterns from diverse data, facilitating zero-shot generalization across urban environments. OpenCity integrates Transformers with graph neural networks to capture complex spatio-temporal dependencies in traffic data. By pre-training OpenCity on large-scale, heterogeneous traffic data from web platforms, we enable the model to learn rich, generalizable representations that can be seamlessly applied to a wide range of traffic forecasting scenarios. Experiments show OpenCity excels in zero-shot prediction and exhibits scaling laws, highlighting its potential as a universal one-for-all traffic prediction solution adaptable to new urban contexts with minimal overhead. Source codes are available at: https://github.com/HKUDS/OpenCity

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IJCAI Conference 2021 Conference Paper

Pattern-enhanced Contrastive Policy Learning Network for Sequential Recommendation

Xiaohai Tong
Pengfei Wang
Chenliang Li
Long Xia
Shaozhang Niu

Sequential recommendation aims to predict users’ future behaviors given their historical interactions. However, due to the randomness and diversity of a user’s behaviors, not all historical items are informative to tell his/her next choice. It is obvious that identifying relevant items and extracting meaningful sequential patterns are necessary for a better recommendation. Unfortunately, few works have focused on this sequence denoising process. In this paper, we propose a PatteRn-enhanced ContrAstive Policy Learning Network (RAP for short) for sequential recommendation, RAP formalizes the denoising problem in the form of Markov Decision Process (MDP), and sample actions for each item to determine whether it is relevant with the target item. To tackle the lack of relevance supervision, RAP fuses a series of mined sequential patterns into the policy learning process, which work as a prior knowledge to guide the denoising process. After that, RAP splits the initial item sequence into two disjoint subsequences: a positive subsequence and a negative subsequence. At this, a novel contrastive learning mechanism is introduced to guide the sequence denoising and achieve preference estimation from the positive subsequence simultaneously. Extensive experiments on four public real-world datasets demonstrate the effectiveness of our approach for sequential recommendation.

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TIST Journal 2017 Journal Article

Directly Optimize Diversity Evaluation Measures

Jun Xu
Long Xia
Yanyan Lan
Jiafeng Guo
Xueqi Cheng

The queries issued to search engines are often ambiguous or multifaceted, which requires search engines to return diverse results that can fulfill as many different information needs as possible; this is called search result diversification. Recently, the relational learning to rank model, which designs a learnable ranking function following the criterion of maximal marginal relevance, has shown effectiveness in search result diversification [Zhu et al. 2014]. The goodness of a diverse ranking model is usually evaluated with diversity evaluation measures such as α-NDCG [Clarke et al. 2008], ERR-IA [Chapelle et al. 2009], and D#-NDCG [Sakai and Song 2011]. Ideally the learning algorithm would train a ranking model that could directly optimize the diversity evaluation measures with respect to the training data. Existing relational learning to rank algorithms, however, only train the ranking models by optimizing loss functions that loosely relate to the evaluation measures. To deal with the problem, we propose a general framework for learning relational ranking models via directly optimizing any diversity evaluation measure. In learning, the loss function upper-bounding the basic loss function defined on a diverse ranking measure is minimized. We can derive new diverse ranking algorithms under the framework, and several diverse ranking algorithms are created based on different upper bounds over the basic loss function. We conducted comparisons between the proposed algorithms with conventional diverse ranking methods using the TREC benchmark datasets. Experimental results show that the algorithms derived under the diverse learning to rank framework always significantly outperform the state-of-the-art baselines.

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