SangKeun Lee

Handling Selfishness in Replica Allocation over a Mobile Ad Hoc Network

In a mobile ad hoc network, the mobility and resource constraints of mobile nodes may lead to network partitioning or performance degradation. Several data replication techniques have been proposed to minimize performance degradation. Most of them assume that all mobile nodes collaborate fully in terms of sharing their memory space. In reality, however, some nodes may selfishly decide only to cooperate partially, or not at all, with other nodes. These selfish nodes could then reduce the overall data accessibility in the network. In this paper, we examine the impact of selfish nodes in a mobile ad hoc network from the perspective of replica allocation. We term this selfish replica allocation. In particular, we develop a selfish node detection algorithm that considers partial selfishness and novel replica allocation techniques to properly cope with selfish replica allocation. The conducted simulations demonstrate the proposed approach outperforms traditional cooperative replica allocation techniques in terms of data accessibility, communication cost, and average query delay.

An effective, efficient XML data broadcasting method in a mobile wireless network

With the rapidly increasing popularity of XML, an effective method to transmit XML data over wireless broadcasting environments is urgently required. In this paper, a novel XML data streaming method for wireless broadcasting environments, is proposed. An XML stream is organized to enable a selective access scheme for simple XPath queries, by borrowing the path summary technique, which was originally devised for indexing semi-structured data. In order to utilize structure information as an XML stream index, the structure information and text values of an XML document are separated. In experimental results, the proposed method demonstrates superior performance over previous approaches with regard to both access and tuning time.

In-Network Processing for Skyline Queries in Sensor Networks

Wireless sensor networks can be used in various fields, e.g., military and civil applications. The technique of saving energy to prolong the life of sensor nodes is one of main challenges to resource-constrained sensor networks. Therefore, in-network aggregation of data has been proposed in resource-constrained environments for energy efficiency. Most previous works on in-network aggregation only support a one-dimensional data (e.g., MIN and MAX). To support a multi-dimensional data, the skyline query is used. The skyline query returns a set of points that are not dominated by any other point on all dimensions. The majority of previous skyline query processing methods (e.g., BNL and BBS) work on centralized storage. Centralized query processing methods do not have merits in terms of energy efficiency in high event rate environments. In this paper, we propose new algorithm of in-network processing for the skyline queries. The proposed algorithm reduces the communication cost and evenly distributes load. The experimental results show the advantages of our algorithm over in-network aggregation in terms of improving energy efficiency.

Semantic contextual advertising based on the open directory project

Contextual advertising seeks to place relevant textual ads within the content of generic webpages. In this article, we explore a novel semantic approach to contextual advertising. This consists of three tasks: (1) building a well-organized hierarchical taxonomy of topics, (2) developing a robust classifier for effectively finding the topics of pages and ads, and (3) ranking ads based on the topical relevance to pages. First, we heuristically build our own taxonomy of topics from the Open Directory Project (ODP). Second, we investigate how to increase classification accuracy by taking the unique characteristics of the ODP into account. Last, we measure the topical relevance of ads by applying a link analysis technique to the similarity graph carefully derived from our taxonomy. Experiments show that our classification method improves the performance of Ma-F1 by as much as 25.7% over the baseline classifier. In addition, our ranking method enhances the relevance of ads substantially, up to 10% in terms of precision at k, compared to a representative strategy.

Supporting transactional cache consistency in mobile database systems

In a mobile computing environment, caching of frequently accessed data has been shown to be a useful technique for reducing contention on the narrow bandwidth of the wireless channels. However, the traditional client/server strategies for supporting transactional cache consistency that require extensive communications between a client and a server are not appropriate in a mobile computing environment. In this paper, we propose a new protocol, called OCC-UTS (Optimisitic Concurrency Control with Update TimeStamp), to support transactional cache consistency in a wireless mobile computing environment by utilizing the broadcast-based solutions for the problem of invalidating caches. The consistency check on accessed data and the commitment protocol are implemented in a truly distributed fashion as an integral part of cache invalidation process, with most burden of consistency check being downloaded to mobile clients. Also, our esperiments based on an analytical model substantiate the basic idea and study the performance characteristics. Experimental results show that OCC-UTS protocol without local cache outperforms other competitor protocol, and the more frequent a mobile client accesses data items the more efficient OCC-UTS protocol with local cache is. With respect to disconnection, a mobile client aborts its transaction if it disconnects more than the invalidation broadcast window size. Thus, the tolerance to disconnection is improved if the invalidation broadcast window size is extended.

A Binary String Approach for Updates in Dynamic Ordered XML Data

To facilitate XML query processing, several labeling schemes have been proposed, in which the ancestor-descendant and parent-child relationships in XML queries can be quickly determined without accessing the original XML file. However, all of these existing schemes have to relabel the existing nodes or recalculate certain values when order-sensitive updates cause insertions, thus causing the label update cost to be high. In this paper, we propose a novel labeling scheme, called IBSL (Improved Binary String Labeling), which supports order-sensitive updates without relabeling or recalculation. In addition, we reuse the deleted labels at the same position in the XML tree. The conducted experimental results show that IBSL efficiently processes order-sensitive queries and leaf node/subtree updates.

Joint multi-grain topic sentiment

The availability of electronic word-of-mouth, online consumer reviews, is increasing rapidly. Users frequently look for important aspects of a product or service in the reviews. They are typically interested in sentiment-oriented ratable aspects (i.e., semantic aspects). However, extracting semantic aspects across domains is challenging. We propose a domain-independent topic sentiment model called Joint Multi-grain Topic Sentiment (JMTS) to extract semantic aspects. JMTS effectively extracts quality semantic aspects automatically, thereby eliminating the requirement for manual probing. We conduct both qualitative and quantitative comparisons to evaluate JMTS. The experimental results confirm that JMTS generates semantic aspects with correlated top words and outperforms state-of-the-art models in several performance metrics.

On the efficiency of secure XML broadcasting

Secure broadcasting of web documents is becoming a crucial requirement for many web-based applications. Under the broadcast document dissemination strategy, a web document source periodically broadcasts (portions of) its documents to a potentially large community of users, without the need for explicit requests. By secure broadcasting, we mean that the delivery of information to users must obey the access control policies of the document source. Traditional access control mechanisms that have been adapted for XML documents, however, do not address the performance issues inherent in access control. In this paper, a labeling scheme is proposed to support rapid reconstruction of XML documents in the context of a well-known method, called XML pool encryption. The proposed labeling scheme supports the speedy inference of structure information in all portions of the document. The binary representation of the proposed labeling scheme is also investigated. In the experimental results, the proposed labeling scheme is efficient in searching for the location of decrypted information.

Efficient, Energy Conserving Transaction Processing in Wireless Data Broadcast

Broadcasting in wireless mobile computing environments is an effective technique to disseminate information to a massive number of clients equipped with powerful, battery operated devices. To conserve the usage of energy, which is a scarce resource, the information to be broadcast must be organized so that the client can selectively tune in at the desired portion of the broadcast. In this paper, the efficient, energy conserving transaction processing in mobile broadcast environments is examined with widely accepted approaches to indexed data organizations suited for a single item retrieval. The basic idea is to share the index information on multiple data items based on the predeclaration technique. The analytical and simulation studies have been performed to evaluate the effectiveness of our methodology, showing that predeclaration-based transaction processing with selective tuning ability can provide a significant performance improvement of battery life, while retaining a low access time. Tolerance to access failures during transaction processing is also described

Using predeclaration for efficient read-only transaction processing in wireless data broadcast

Wireless data broadcast allows a large number of users to retrieve data simultaneously in mobile databases, resulting in an efficient way of using the scarce wireless bandwidth. However, the efficiency of data access methods is limited by an inherent property that data can only be accessed strictly sequentially by users. To properly cope with the inherent property, this paper presents three predeclaration-based transaction processing methods that yield a significant performance improvement in wireless data broadcast.