Xueyan Tang Associate Professor
		College of Computing and Data Science Nanyang Technological University Nanyang Avenue Singapore 639798					Office: N4-02a-08 Tel: (+65) 6790-5356 Fax: (+65) 6792-6559

Research Position Openings (Distributed Computing, Submodular Optimization)

Short Biography

Xueyan Tang is currently an Associate Professor in the College of Computing and Data Science at Nanyang Technological University, Singapore. He received his Ph.D. degree in Computer Science from the Hong Kong University of Science and Technology in 2003, and his B.Eng. degree in Computer Science and Engineering from Shanghai Jiao Tong University in 1998. Prior to his undergraduate study, he received his secondary education in the No.2 Secondary School Attached to East China Normal University from 1988 to 1994.

Research Interests

Distributed systems, cloud computing, resource allocation.

Professional Activities

• Associate Editor, IEEE Transactions on Cloud Computing (2021-present)
• Associate Editor, IEEE Transactions on Parallel and Distributed Systems (2010-2014)
• Program Co-Chair, ICPADS'2012, CloudCom'2014, ICDCS'2020
• TPC Member, INFOCOM'2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021, 2022
• TPC Member, ICDCS'2012, 2015, 2022, 2023, 2024
• TPC Member, ICDE'2010, 2011
• TPC Member, SPAA'2021
• TPC Member, IPDPS'2024

Selected Publications

Note: To download papers from the ACM Digital Library with its Author-Izer Service, please ensure that you are accessing this page at the URL of http://personal.ntu.edu.sg/asxytang/

• T. Zuo, X. Tang, and B. S. Lee. Cost-Driven Data Replication with Predictions. Accepted to appear in the 36th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), June 2024.

• M. Liu and X. Tang. Brief Announcement: Scheduling Jobs for Minimum Span: Improved Bounds and Learning-Augmented Algorithms. Accepted to appear in the 36th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), June 2024.

• M. Liu and X. Tang. Brief Announcement: Tight bounds for Dynamic Bin Packing with Predictions. Accepted to appear in the 36th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), June 2024.

• T. Zuo, X. Tang, and B. S. Lee. A Randomized Caching Algorithm for Distributed Data Access. Accepted to appear in the 43rd IEEE Conference on Computer Communications (INFOCOM), May 2024.

• X. He, X. Tang, W. Cai, and J. Li. A Stochastic Process Approach for Multi-agent Path Finding with Non-asymptotic Performance Guarantees. Artificial Intelligence, vol. 329, article no. 104084, pp. 1-30, April 2024.

• Y. Zhu, J. Tang, X. Tang, S. Wang, and A. Lim. 2-hop+ Sampling: Efficient and Effective Influence Estimation. IEEE Transactions on Knowledge and Data Engineering, vol. 35, no. 2, pp. 1088-1103, February 2023.

• M. Liu and X. Tang. Busy-Time Scheduling on Heterogeneous Machines: Algorithms and Analysis. IEEE Transactions on Parallel and Distributed Systems, vol. 33, no. 12, pp. 3942-3958, December 2022.

• M. Liu and X. Tang. Dynamic Bin Packing with Predictions. Proceedings of the ACM on Measurement and Analysis of Computing Systems, vol. 6, issue 3, article no. 45, pp. 1-24, December 2022. Abstract in Proceedings of the 2023 ACM SIGMETRICS / International Conference on Measurement and Modeling of Computer Systems, pp. 57-58, June 2023.

• Y. Zhu, J. Tang, and X. Tang. Optimal Price Profile for Influential Nodes in Online Social Networks. The VLDB Journal, vol. 31, no. 4, pp. 779-795, July 2022.

• Y. Guan and X. Tang. On Task Assignment and Scheduling for Distributed Job Execution. In Proceedings of the 22nd IEEE/ACM International Symposium on Cluster, Cloud and Internet Computing (CCGrid), pp. 726-735, May 2022.

• J. Tang, Y. Zhu, X. Tang, and K. Han. Distributed Influence Maximization for Large-Scale Online Social Networks. In Proceedings of the 38th IEEE International Conference on Data Engineering (ICDE), pp. 81-95, May 2022.

• Y. Zhu, J. Tang, X. Tang, and L. Chen. Analysis of Influence Contribution in Social Advertising. In Proceedings of the VLDB Endowment, vol. 15, no. 2, pp. 348-360, October 2021.

• X. Wu, Y. Liu, X. Tang, W. Cai, F. Bai, G. Khonstantine, and G. Zhao. Multi-Agent Pickup and Delivery with Task Deadlines. In Proceedings of the 20th IEEE/WIC/ACM International Conference on Web Intelligence and Intelligent Agent Technology (WI-IAT), pp. 360-367, December 2021.

• R. Ren and X. Tang. Generalized Skyline Interval Coloring and Dynamic Geometric Bin Packing Problems. In Proceedings of the 50th International Conference on Parallel Processing (ICPP), article no. 52, pp. 1-10, August 2021. [Presentation]

• M. Liu and X. Tang. Analysis of Busy-Time Scheduling on Heterogeneous Machines. In Proceedings of the 33rd ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), pp. 340-350, July 2021. [Presentation]

• J. Tang, X. Tang, A. Lim, K. Han, C. Li, and J. Yuan. Revisiting Modified Greedy Algorithm for Monotone Submodular Maximization with a Knapsack Constraint. Proceedings of the ACM on Measurement and Analysis of Computing Systems, vol. 5, issue 1, article no. 08, pp. 1-22, March 2021. Abstract in Proceedings of the 2021 ACM SIGMETRICS / International Conference on Measurement and Modeling of Computer Systems, pp. 63-64, May 2021.

• Y. Li, C. Zhao, X. Tang, W. Cai, X. Liu, G. Wang, and X. Gong. Towards Minimizing Resource Usage with QoS Guarantee in Cloud Gaming. IEEE Transactions on Parallel and Distributed Systems, vol. 32, no. 2, pp. 426-440, February 2021.

• R. Ren, Y. Zhu, C. Li, and X. Tang. Interval Job Scheduling with Machine Launch Cost. IEEE Transactions on Parallel and Distributed Systems, vol. 31, no. 12, pp. 2776-2788, December 2020.

• Y. Zhu, J. Tang, and X. Tang. Pricing Influential Nodes in Online Social Networks. In Proceedings of the VLDB Endowment, vol. 13, no. 10, pp. 1614-1627, June 2020.

• R. Ren and X. Tang. Busy-Time Scheduling on Heterogeneous Machines. In Proceedings of the 34th IEEE International Parallel and Distributed Processing Symposium (IPDPS), pp. 306-315, May 2020.

• C. Li and X. Tang. On Fault-Tolerant Bin Packing for Online Resource Allocation. IEEE Transactions on Parallel and Distributed Systems, vol. 31, no. 4, pp. 817-829, April 2020.

• Y. Li, X. Tang, W. Cai, J. Tong, X. Liu, and G. Wang. Resource-Efficient Index Shard Replication in Large Scale Search Engines. IEEE Transactions on Parallel and Distributed Systems, vol. 30, no. 12, pp. 2820-2835, December 2019.

• Y. Guan, C. Li, and X. Tang. On Max-min Fair Resource Allocation for Distributed Job Execution. In Proceedings of the 48th International Conference on Parallel Processing (ICPP), article no. 55, pp. 1-10, August 2019.

• M. M. Tan, R. Ren, and X. Tang. Cloud Scheduling with Discrete Charging Units. IEEE Transactions on Parallel and Distributed Systems, vol. 30, no. 7, pp. 1541-1551, July 2019.

• J. Tang, K. Huang, X. Xiao, L. V. S. Lakshmanan, X. Tang, A. Sun, and A. Lim. Efficient Approximation Algorithms for Adaptive Seed Minimization. In Proceedings of the 2019 ACM SIGMOD International Conference on Management of Data (SIGMOD), pp. 1096-1113, July 2019.

• Y. Li, C. Shan, R. Chen, X. Tang, W. Cai, S. Tang, X. Liu, G. Wang, X. Gong, and Y. Zhang. GAugur: Quantifying Performance Interference of Colocated Games for Improving Resource Utilization in Cloud Gaming. In Proceedings of the 28th ACM International Symposium on High-Performance Parallel and Distributed Computing (HPDC), pp. 231-242, June 2019.

• Y. Li, Y. Deng, X. Tang, W. Cai, X. Liu, and G. Wang. Cost-Efficient Server Provisioning for Cloud Gaming. ACM Transactions on Multimedia Computing, Communications, and Applications, vol. 14, issue 3s, article no. 55, pp. 1-22, August 2018.

• Y. Li, X. Tang, W. Cai, J. Tong, X. Liu, G. Wang, C. Gao, X. Cao, G. Geng, and M. Li. Index Shard Replication Strategies for Improving Resource Utilization in Large Scale Search Engines. In Proceedings of the 47th International Conference on Parallel Processing (ICPP), article no. 84, pp. 1-10, August 2018.

• J. Tang, X. Tang, and J. Yuan. Profit Maximization for Viral Marketing in Online Social Networks: Algorithms and Analysis. IEEE Transactions on Knowledge and Data Engineering, vol. 30, no. 6, pp. 1095-1108, June 2018.

• J. Tang, X. Tang, X. Xiao, and J. Yuan. Online Processing Algorithms for Influence Maximization. In Proceedings of the 2018 ACM SIGMOD International Conference on Management of Data (SIGMOD), pp. 991-1005, June 2018.

• Y. Deng, Y. Li, R. Seet, X. Tang, and W. Cai. The Server Allocation Problem for Session-based Multiplayer Cloud Gaming. IEEE Transactions on Multimedia, vol. 20, no. 5, pp. 1233-1245, May 2018.

• J. Tang, X. Tang, and J. Yuan. Traffic-Optimized Data Placement for Social Media. IEEE Transactions on Multimedia, vol. 20, no. 4, pp. 1008-1023, April 2018.

• J. Tang, X. Tang, and J. Yuan. Towards Profit Maximization for Online Social Network Providers. In Proceedings of the 37th IEEE Conference on Computer Communications (INFOCOM), pp. 1178-1186, April 2018. [Full Version]

• Y. Li, Y. Deng, X. Tang, W. Cai, X. Liu, and G. Wang. On Server Provisioning for Cloud Gaming. In Proceedings of the 25th ACM International Conference on Multimedia (MM), pp. 492-500, October 2017.

• J. Tang, X. Tang, and J. Yuan. Influence Maximization Meets Efficiency and Effectiveness: A Hop-Based Approach. In Proceedings of the 9th IEEE/ACM International Conference on Advances in Social Networks Analysis and Mining (ASONAM), pp. 64-71, August 2017. [Full Version]

• R. Ren and X. Tang. Online Flexible Job Scheduling for Minimum Span. In Proceedings of the 29th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), pp. 55-66, July 2017.

• C. Li and X. Tang. Brief Announcement: Towards Fault-Tolerant Bin Packing for Online Cloud Resource Allocation. In Proceedings of the 29th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), pp. 231-233, July 2017.

• Q. Wang, M. M. Tan, X. Tang, and W. Cai. Minimizing Cost in IaaS Clouds via Scheduled Instance Reservation. In Proceedings of the 37th IEEE International Conference on Distributed Computing Systems (ICDCS), pp. 1565-1574, June 2017.

• R. Ren, X. Tang, Y. Li, and W. Cai. Competitiveness of Dynamic Bin Packing for Online Cloud Server Allocation. IEEE/ACM Transactions on Networking, vol. 25, no. 3, pp. 1324-1331, June 2017.

• L. Zhang, X. Tang, and B. He. Analysis of Minimum Interaction Time for Continuous Distributed Interactive Computing. IEEE Transactions on Parallel and Distributed Systems, vol. 28, no. 2, pp. 401-415, February 2017.

• J. Tang, X. Tang, and J. Yuan. Profit Maximization for Viral Marketing in Online Social Networks. In Proceedings of the 24th IEEE International Conference on Network Protocols (ICNP), 10 pages, November 2016.

• Y. Deng, Y. Li, X. Tang, and W. Cai. Server Allocation for Multiplayer Cloud Gaming. In Proceedings of the 24th ACM International Conference on Multimedia (MM), pp. 918-927, October 2016.

• R. Ren and X. Tang. Clairvoyant Dynamic Bin Packing for Job Scheduling with Minimum Server Usage Time. In Proceedings of the 28th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), pp. 227-237, July 2016. [Appendix]

• X. Tang, Y. Li, R. Ren, and W. Cai. On First Fit Bin Packing for Online Cloud Server Allocation. In Proceedings of the 30th IEEE International Parallel and Distributed Processing Symposium (IPDPS), pp. 323-332, May 2016.

• S. Chen, S. Jiang, B. He, and X. Tang. A Study of Sorting Algorithms on Approximate Memory. In Proceedings of the 2016 ACM SIGMOD International Conference on Management of Data (SIGMOD), pp. 647-662, June 2016.

• H. Zheng and X. Tang. The Server Provisioning Problem for Continuous Distributed Interactive Applications. IEEE Transactions on Parallel and Distributed Systems, vol. 27, no. 1, pp. 271-285, January 2016.

• Y. Li, X. Tang, and W. Cai. Dynamic Bin Packing for On-Demand Cloud Resource Allocation. IEEE Transactions on Parallel and Distributed Systems, vol. 27, no. 1, pp. 157-170, January 2016.

• Y. Lu, D. Wu, B. He, X. Tang, J. Xu, and M. Guo. Rank-Aware Dynamic Migrations and Adaptive Demotions for DRAM Power Management. IEEE Transactions on Computers, vol. 65, no. 1, pp. 187-202, January 2016. [Appendix]

• Y. Li, X. Tang, and W. Cai. Play Request Dispatching for Efficient Virtual Machine Usage in Cloud Gaming. IEEE Transactions on Circuits and Systems for Video Technology, vol. 25, no. 12, pp. 2052-2063, December 2015.

• Y. Li, Y. Deng, R. Seet, X. Tang, and W. Cai. MASTER: Multi-platform Application Streaming Toolkits for Elastic Resources. In Proceedings of the 23rd ACM International Conference on Multimedia (MM), pp. 805-806, October 2015.

• H. Zheng and X. Tang. Analysis of Server Provisioning for Distributed Interactive Applications. IEEE Transactions on Computers, vol. 64, no. 10, pp. 2752-2766, October 2015. [Appendix]

• Y. Lu, B. He, X. Tang, and M. Guo. Synergy of Dynamic Frequency Scaling and Demotion on DRAM Power Management: Models and Optimizations. IEEE Transactions on Computers, vol. 64, no. 8, pp. 2367-2381, August 2015. [Appendix]

• J. Tang, X. Tang, and J. Yuan. Optimizing Inter-Server Communication for Online Social Networks. In Proceedings of the 35th IEEE International Conference on Distributed Computing Systems (ICDCS), pp. 215-224, June 2015.

• Y. Li, X. Tang, and W. Cai. Let's Depart Together: Efficient Play Request Dispatching in Cloud Gaming. In Proceedings of the 13th Annual International Workshop on Network and Systems Support for Games (NetGames), 6 pages, December 2014.

• Y. Li, X. Tang, and W. Cai. On Dynamic Bin Packing for Resource Allocation in the Cloud. In Proceedings of the 26th ACM Symposium on Parallelism in Algorithms and Architectures (SPAA), pp. 2-11, June 2014.

• L. Zhang and X. Tang. The Client Assignment Problem for Continuous Distributed Interactive Applications: Analysis, Algorithms, and Evaluation. IEEE Transactions on Parallel and Distributed Systems, vol. 25, no. 3, pp. 785-795, March 2014.

• L. Zhang, X. Tang, and B. He. Brief Announcement: On Minimum Interaction Time for Continuous Distributed Interactive Computing. In Proceedings of the 32nd Annual ACM Symposium on Principles of Distributed Computing (PODC), pp. 122-124, July 2013.

• H. Zheng and X. Tang. On Server Provisioning for Distributed Interactive Applications. In Proceedings of the 33rd IEEE International Conference on Distributed Computing Systems (ICDCS), pp. 500-509, July 2013.

• K. Pan, X. Tang, W. Cai, S. Zhou and H. Zheng. Hierarchical Interest Management for Distributed Virtual Environments. In Proceedings of the 2013 ACM SIGSIM Conference on Principles of Advanced Discrete Simulation (SIGSIM PADS), pp. 137-146, May 2013.

• W. Zhao and X. Tang. Scheduling Sensor Data Collection with Dynamic Traffic Patterns. IEEE Transactions on Parallel and Distributed Systems, vol. 24, no. 4, pp. 789-802, April 2013.

• C. Chen, B. He, X. Tang, C. Chen, and Y. Liu. Green Databases Through Integration of Renewable Energy. In Proceedings of the 6th Biennial Conference on Innovative Data Systems Research (CIDR), 11 pages, January 2013.

• L. Zhang and X. Tang. Optimizing Client Assignment for Enhancing Interactivity in Distributed Interactive Applications. IEEE/ACM Transactions on Networking, vol. 20, no. 6, pp. 1707-1720, December 2012.

• C. Chen, B. He, and X. Tang. Green-Aware Workload Scheduling in Geographically Distributed Data Centers. In Proceedings of the 4th IEEE International Conference on Cloud Computing Technology and Science (CloudCom), pp. 82-89, December 2012.

• D. Wu, B. He, X. Tang, J. Xu, and M. Guo. RAMZzz: Rank-Aware DRAM Power Management with Dynamic Migrations and Demotions. In Proceedings of the 2012 ACM/IEEE International Conference for High Performance Computing, Networking, Storage and Analysis (SC), article no. 32, 11 pages, November 2012.

• D. Ta, T. Nguyen, S. Zhou, X. Tang, W. Cai, and R. Ayani. Interactivity-Constrained Server Provisioning in Large-Scale Distributed Virtual Environments. IEEE Transactions on Parallel and Distributed Systems, vol. 23, no. 2, pp. 304-312, February 2012.

• L. Zhang and X. Tang. The Client Assignment Problem for Continuous Distributed Interactive Applications. In Proceedings of the 31st IEEE International Conference on Distributed Computing Systems (ICDCS), pp. 203-214, June 2011.

• W. Zhao and X. Tang. Scheduling Data Collection with Dynamic Traffic Patterns in Wireless Sensor Networks. In Proceedings of the 30th IEEE Conference on Computer Communications (INFOCOM), pp. 286-290, April 2011.

• L. Zhang and X. Tang. Client Assignment for Improving Interactivity in Distributed Interactive Applications. In Proceedings of the 30th IEEE Conference on Computer Communications (INFOCOM), pp. 3227-3235, April 2011.

• X. Tang and S. Zhou. Update Scheduling for Improving Consistency in Distributed Virtual Environments. IEEE Transactions on Parallel and Distributed Systems, vol. 21, no. 6, pp. 765-777, June 2010.

• K. Pan, W. Cai, X. Tang, S. Zhou, and S. J. Turner. A Hybrid Interest Management Mechanism for Peer-to-Peer Networked Virtual Environments. In Proceedings of the 24th IEEE International Parallel and Distributed Processing Symposium (IPDPS), 12 pages, April 2010.

• J. Xu, X. Tang, H. Hu and J. Du. Privacy-Conscious Location-Based Queries in Mobile Environments. IEEE Transactions on Parallel and Distributed Systems, vol. 21, no. 3, pp. 313-326, March 2010.

• Y. Yao, X. Tang, and E.-P. Lim. Localized Monitoring of kNN Queries in Wireless Sensor Networks. The VLDB Journal, vol. 18, no. 1, pp. 99-117, January 2009.

• X. Tang, J. Xu, and W.-C. Lee. Analysis of TTL-Based Consistency in Unstructured Peer-to-Peer Networks. IEEE Transactions on Parallel and Distributed Systems, vol. 19, no. 12, pp. 1683-1694, December 2008.

• X. Tang and J. Xu. Optimizing Lifetime for Continuous Data Aggregation with Precision Guarantees in Wireless Sensor Networks. IEEE/ACM Transactions on Networking, vol. 16, no. 4, pp. 904-917, August 2008.

• X. Tang and J. Xu. Adaptive Data Collection Strategies for Lifetime-Constrained Wireless Sensor Networks. IEEE Transactions on Parallel and Distributed Systems, vol. 19, no. 6, pp. 721-734, June 2008.

• J. Xu, X. Tang, and W.-C. Lee. A New Storage Scheme for Approximate Location Queries in Object Tracking Sensor Networks. IEEE Transactions on Parallel and Distributed Systems, vol. 19, no. 2, pp. 262-275, February 2008.

• M. Wu, J. Xu, X. Tang, and W.-C. Lee. Top-k Monitoring in Wireless Sensor Networks. IEEE Transactions on Knowledge and Data Engineering, vol. 19, no. 7, pp. 962-976, July 2007.

• X. Tang, H. Chi, and S. T. Chanson. Optimal Replica Placement under TTL-Based Consistency. IEEE Transactions on Parallel and Distributed Systems, vol. 18, no. 3, pp. 351-363, March 2007.

• X. Tang and S. T. Chanson. Analysis of Replica Placement under Expiration-Based Consistency Management. IEEE Transactions on Parallel and Distributed Systems, vol. 17, no. 11, pp. 1253-1263, November 2006.

• Y. Yao, X. Tang, E.-P. Lim, and A. Sun. An Energy-Efficient and Access Latency Optimized Indexing Scheme for Wireless Data Broadcast. IEEE Transactions on Knowledge and Data Engineering, vol. 18, no. 8, pp. 1111-1124, August 2006.

• X. Tang and J. Xu. Extending Network Lifetime for Precision-Constrained Data Aggregation in Wireless Sensor Networks. In Proceedings of the 25th IEEE Conference on Computer Communications (INFOCOM), pp. 755-766, April 2006.

• J. Xu, W.-C. Lee, X. Tang, Q. Gao, and S. Li. An Error-Resilient and Tunable Distributed Indexing Scheme for Wireless Data Broadcast. IEEE Transactions on Knowledge and Data Engineering, vol. 18, no. 3, pp. 392-404, March 2006.

• J. Xu, X. Tang, and W.-C. Lee. Time-Critical On-Demand Data Broadcast: Algorithms, Analysis, and Performance Evaluation. IEEE Transactions on Parallel and Distributed Systems, vol. 17, no. 1, pp. 3-14, January 2006.

• X. Tang and J. Xu. QoS-Aware Replica Placement for Content Distribution. IEEE Transactions on Parallel and Distributed Systems, vol. 16, no. 10, pp. 921-932, October 2005.

• J. Xu, W.-C. Lee, and X. Tang. Exponential Index: A Parameterized Distributed Indexing Scheme for Data on Air. In Proceedings of the 2nd ACM/USENIX International Conference on Mobile Systems, Applications, and Services (MobiSys), pp. 153-164, June 2004.

• X. Tang and S. T. Chanson. Minimal Cost Replication of Dynamic Web Contents under Flat Update Delivery. IEEE Transactions on Parallel and Distributed Systems, vol. 15, no. 5, pp. 431-439, May 2004.

• X. Tang and S. T. Chanson. The Minimal Cost Distribution Tree Problem for Recursive Expiration-Based Consistency Management. IEEE Transactions on Parallel and Distributed Systems, vol. 15, no. 3, pp. 214-227, March 2004.

• J. Xu, X. Tang, and D. L. Lee. Performance Analysis of Location-Dependent Cache Invalidation Schemes for Mobile Environments. IEEE Transactions on Knowledge and Data Engineering, vol. 15, no. 2, pp. 474-488, March/April 2003.

• X. Tang and S. T. Chanson. Coordinated En-Route Web Caching. IEEE Transactions on Computers, vol. 51, no. 6, pp. 595-607, June 2002.

Copyright Notice: This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.

IEEE Copyright Notice: ?200x IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.

ACM Copyright Notice: Copyright ? YYYY by the Association for Computing Machinery, Inc. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from Publications Dept., ACM, Inc., fax +1 (212) 869-0481, or permissions@acm.org.