Browsing by Author "Wu, MY"

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A hypergraph based approach to declustering problems
(2001)
Liu, DR
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Wu, MY
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Parallelizing I/O operations via effective declustering of data is becoming essential to scale up the performance of parallel databases or high performance systems. Declustering has been shown to be a NP-complete problem in some contexts. Some heuristic methods have been proposed to solve this problem. However, most methods are not effective in several cases such as queries with different access frequencies or data with different sizes. In this paper, we propose a hypergraph model to formulate the declustering problem. Several interesting theoretical results are achieved by analyzing the proposed model. The proposed approach will allow modeling a wide range of declustering problems. Furthermore, the hypergraph declustering model is used as the basis to develop new heuristic methods, including a greedy method and a hybrid declustering method. Experiments show that the proposed methods can achieve better performance than several declustering methods.
Role-based authorizations for workflow systems in support of task-based separation of duty
(2004-11-01)
Liu, DR
;
Wu, MY
;
Lee, ST
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資訊管理與財務金融系註：原資管所+財金所
;
Department of Information Management and Finance
Role-based authorizations for assigning tasks of workflows to roles/users are crucial to security management in workflow management systems. The authorizations must enforce separation of duty (SoD) constraints to prevent fraud and errors. This work analyzes and defines several duty-conflict relationships among tasks, and designs authorization rules to enforce SoD constraints based on the analysis. A novel authorization model that incorporates authorization rules is then proposed to support the planning of assigning tasks to roles/users, and the run-time activation of tasks. Different from existing work, the proposed authorization model considers the AND/XOR split structures of workflows and execution dependency among tasks to enforce separation of duties in assigning tasks to roles/users. A prototype system is developed to realize the effectiveness of the proposed authorization model. (C) 2003 Elsevier Inc. All rights reserved.