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Liu, Ling

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Publication Search Results

Now showing 1 - 6 of 6
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    PeerTrust: A Trust Mechanism for an Open Peer-to-Peer Information System
    (Georgia Institute of Technology, 2002) Xiong, Li ; Liu, Ling
    In an open peer-to-peer information system, peers often have to interact with unknown or unfamiliar peers and need to manage the risk that is involved with the interactions without any presence of trusted third parties or trust authorities. It is important for peers to be able to reason about trust when interacting with each other to accomplish a task. This paper presents PeerTrust, a simple and yet effective trust mechanism for quantifying and comparing the trustworthiness of peers. We argue that the amount of satisfaction a peer obtains through interactions, the total number of interactions that a peer has with other peers, and the balancing factor of trust all play a crucial role in evaluating the trustworthiness of the peer. This paper also discusses the architecture and the design considerations in implementing this mechanism in a decentralized peer-to-peer system. We report the set of initial experiments, showing the feasibility, the cost, and the benefit of our approach.
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    A New Document Placement Scheme for Cooperative Caching on the Internet
    (Georgia Institute of Technology, 2002) Ramaswamy, Lakshmish Macheeri ; Liu, Ling
    The sharing of caches among proxies is an important technique to reduce Web traffic, alleviate network bottlenecks and improve response time of document requests. Most existing work on cooperative caching has been focused on serving misses collaboratively. Very few have studied the effect of cooperation on document placement schemes and its potential enhancements on cache hit ratio and latency reduction. In this paper we propose a new document placement scheme, which takes into account of the contentions at individual caches in order to limit the replication of documents within a cache group and increase document hit ratio. The main idea of this new scheme is to view the aggregate disk space of the cache group as a global resource of the group, and uses the concept of cache expiration age to measure the contention of individual caches. The decision of whether to cache a document at a proxy is made collectively among the caches that already have a copy of this document. We refer to this new document placement scheme as the expiration age based scheme (EA scheme for short). The EA scheme effectively reduces the replication of documents across the cache group, while ensuring that a copy of the document always resides in a cache where it is likely to stay for the longest time. We report our initial study on the potentials and limits of the EA scheme using both analytic modeling and trace-based simulation. The experiments show that the EA scheme yields higher hit rates and better response times compared to the existing document placement schemes used in most of the caching proxies.
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    Distributed Workflow Restructuring: An Experimental Study
    (Georgia Institute of Technology, 2002) Ruiz, Duncan Dubugras ; Liu, Ling ; Pu, Calton
    Workflow systems have been one of the enabling technologies for automation of business processes in corporate enterprises. Many modern production workflows need to incorporate deadline control throughout the workflow management system. However, the increasing volume and diversity of digital information available online and the unpredictable amount of network delays or server failures have led to a growing problem that conventional workflow management systems do not have, namely how to reorganize existing workflow activities in order to meet deadlines in the presence of unexpected delays. We refer to this problem as the workflow-restructuring problem. This paper describes the notation and issues of workflow restructuring, and discusses a set of workflow activity restructuring operators. We illustrate the inherent semantics of these restructuring operators using the Transactional Activity Model (TAM). The paper contains two main contributions. First, we study the environmental instabilities (e.g., resource shortages and network delays) that cause workflows to perform sub-optimally and how workflow restructuring can address this problem. Second, we evaluate the effectiveness of workflow-restructuring operators through simulation. Our initial experiments demonstrate that run-time workflow restructuring can improve response time significantly for unstable environments.
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    PeerCQ: A Scalable and Self-Configurable Peer-to-Peer Information Monitoring System
    (Georgia Institute of Technology, 2002) Gedik, Bugra ; Liu, Ling
    PeerCQ is a peer-to-peer Continual Query system for information monitoring on the Internet. It uses Continual Queries (CQs) as its primitives to express information-monitoring requests. A primary objective of the PeerCQ system is to build a decentralized Internet scale distributed information-monitoring system, which is highly scalable, self-configurable and supports efficient and robust way of processing CQs. In this paper we describe the basic architecture of the PeerCQ system and focus on the mechanisms used for service partitioning and service lookup. There are two unique characteristics of PeerCQ. First, it introduces a donation based peer-aware mechanism for handling the peer heterogeneity. Second, it integrates CQ-aware and peer-aware information into its service partitioning scheme, while maintaining decentralization and self-configurability. We report a set of initial experiments demonstrating the sensitiveness of our approach to peer heterogeneity and the effectiveness of our service partitioning algorithm with respect to load balancing and system utilization.
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    Vista: Looking Into the Clusters in Very Large Multidimensional Datasets
    (Georgia Institute of Technology, 2002) Chen, Keke ; Liu, Ling
    Information Visualization is commonly recognized as a useful method for understanding sophistication in large datasets. In this paper, we introduce an efficient and flexible clustering approach that combines visual clustering and fast disk labelling for very large datasets. This paper has three contributions. First, we propose a framework Vista that incorporates information visualization methods into the clustering process in order to enhance the understanding of the intermediate clustering results and allow user to revise the clustering results before disk labelling phase. Second, we introduce a fast and flexible disk-labelling algorithm ClusterMap, which utilizes the visual clustering result to improve the overall performance of clustering on very large datasets. Third, we develop a visualization model that maps multidimensional dataset to 2D visualization while preserving or partially preserving clusters. Experiments show that Vista combining with ClusterMap, is faster and has lower error rate than existing algorithms for very large datasets. It is also flexible because the "cluster map" can be easily adjusted to meet application-specific clustering requirements.
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    Omini: A Fully Automated Object Extraction System for the World Wide Web
    (Georgia Institute of Technology, 2000) Buttler, David John ; Liu, Ling ; Pu, Calton
    This paper presents a fully automated object extraction system - Omini.A distinct feature of Omini is the suite of algorithms and the automatically learned information extraction rules for discovering and extracting objects from dynamic Web pages or static Web pages that contain multiple object instances. We evaluated the system using more than 2,000 Web pages over 40 sites. It achieves 100% precision (returns only correct objects) and excellent recall (between 93% and 98%, with very few significant objects left out). The object boundary identification algorithms are fast, about 0.1 second per page with a simple optimization.