• Journal of KIISE:Databases
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• v.35 no.3
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• pp.257-271
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• 2008

Wireless broadcast environments has character that a number of mobile client can receive data streaming from central server no matter how they are so many. Because it is asymmetric bandwidth in that uplink and downlink bandwidth are different. This advantage helps wireless broadcast environments is used in many applications. These applications work almost read operation and need control concurrency using transaction unit. Previous concurrency control scheme in single channel is not adapted in multi channel environments because consistency of data are broken when a mobile client tunes in a broadcast cycle in a channel and then move into another channel and listen to different broadcast cycle with already accessed broadcast cycle. In this paper, we propose concurrency control for read-only mobile transactions in multiple wireless broadcast channel. First of all, we adapt index and data dedicated channel and propose LBCPC(Longest Broadcast Cycle Per Channel) as new unit of consistency. In index dedicated channel, it is repeatedly broadcasted data in same BCPC(Broadcast Cycle Per Channel) until LBCPC. And mobile transaction executes validation using control information every LBCPC. As a result, consistency of data is kept and average response time is shorter than one in single channel because waiting time for restart reduces. And as control information is broadcasted more frequently than in single channel, it is guaranteed currency about data accessed by transaction. Finally, according to the simulation result, we verify performance of our scheme in multi channel as comparing average response time with single channel.

• Journal of KIISE:Databases
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• v.32 no.3
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• pp.285-296
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• 2005

In mobile distributed systems the data on the air can be accessed by a lot of mobile clients. And, we need an indexing scheme in order to energy-efficiently access the data on the wireless broadcast stream. In conventional indexing schemes, they use the values of primary key attributes and construct tree-structured index. Therefore, the conventional indexing schemes do not support content-based retrieval queries such as partial-match queries. In this paper we propose an indexing scheme, called B2V-Tree, which supports partial match queries on wireless broadcast data stream. For this purpose, we construct a tree-structured index which is composed of bit-vectors, where the bit-vectors are generated from data records through multi-attribute hashing.

• Journal of KIISE:Databases
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• v.32 no.4
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• pp.394-404
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• 2005

Battery capacity of mobile clients in wireless mobile computing environments is one of the important resources that determine the availability of mobile clients. So, data broadcast techniques in mobile computing environments need not only rapid delivery of requested data but also efficient data delivery mechanisms which can reduce battery consumption of mobile clients. This paper proposes organization of an index and broadcast data for on-demand data broadcast. It organizes an index containing broadcast time of each data using some of high-priority data in a broadcast server. By sending such index information prior to the corresponding data, the proposed approach reduces tuning time of mobile clients. It also includes when the next index information will be broadcasted in each data broadcast. This can reduce tuning time of mobile clients waiting for an index to be broadcasted. Experiments show that the proposed approach effectively reduces tuning time of mobile clients.

• Journal of KIISE:Databases
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• v.29 no.5
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• pp.404-415
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• 2002

In this paper, we address the issue of ensuring consistency of multiple data items requested in a certain order by read-only transactions in a wireless data broadcast environment. To handle the inherent property in a data broadcast environment that data can only be accessed strictly sequential by users, we explore a predeclaration-based query optimization and devise two practical transaction processing methods in the context of local caching. We also evaluate the performance of the proposed methods by an analytical study Evaluation results show that the predeclaration technique we introduce reduces response time significantly and adapts to dynamic changes in workload.

• Journal of KIISE:Software and Applications
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• v.26 no.9
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• pp.1085-1094
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• 1999

이동 분산 환경에서는 무선 데이타 전송 기법을 통하여 사용자들에게 다양한 정보들을 전달하게 된다. 본 논문은 균등 무선 데이타 방송 환경에서, 빠른 시간에 방송데이타를 접근할 수 있는 방법에 대하여 기술한다. 이를 위하여 무선 방송 데이타의 스케쥴링 문제를 정의하고, 어떤 질의가 접근하는 데이타들의 응집 정도를 나타내는 `질의 거리(Query Distance: QD)'라는 측정 기준을 제시한다. 제안한 질의 거리를 사용하여 각 질의의 우선 순위에 따라 해당 질의가 접근하는 데이타 집합을 방송 스케쥴에 추가하면서 스케쥴을 구성하는 데이타 스케쥴링 기법을 제시한다. 데이타 집합의 스케쥴 구성 과정에서 우선 순위가 높은 질의의 질의 거리를 최소화하면서 낮은 우선 순위 질의들의 질의 거리를 줄이는 스케쥴 확장 규칙들을 사용한다. 예를 이용하여 제안하는 방법에 대하여 설명한 후, 실험을 통해 제안한 방법의 성능을 평가한다.Abstract In mobile distributed systems the data on the air can be accessed by a lot of clients. This paper describes the way clients access the broadcast data in short latency in uniform wireless broadcasting environment. We define the problem of wireless data scheduling and propose a measure, named Query Distance(QD), which represents the coherence degree of data set accessed by a query. By using the measure, we give a data scheduling method that constructs the broadcast schedule by appending each query's data set in greedy way. When constructing the schedule, we use schedule expansion rules that reduce the QD's of lower-frequency queries while minimizing the QD's of the higher-frequency ones. With the use of examples we illustrate the mechanism of the proposed method and we test the performance of our method.

• Journal of KIISE:Databases
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• v.36 no.1
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• pp.50-62
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• 2009

In wireless and mobile environments, data broadcasting is recognized as an effective way for data dissemination due to its benefits to bandwidth efficiency, energy-efficiency, and scalability. In this paper, we address the problem of delayed query processing raised by tree-based index structures in wireless broadcast environments, which increases the access time of the mobile clients. We propose a novel distributed index structure and a clustering strategy for streaming XML data which enable energy and latency-efficient broadcast of XML data. We first define the DIX node structure to implement a fully distributed index structure which contains tag name, attributes, and text content of an element as well as its corresponding indices. By exploiting the index information in the DIX node stream, a mobile client can access the wireless stream in a shorter latency. We also suggest a method of clustering DIX nodes in the stream, which can further enhance the performance of query processing over the stream in the mobile clients. Through extensive performance experiments, we demonstrate that our approach is effective for wireless broadcasting of XML data and outperforms the previous methods.

• Journal of KIISE:Information Networking
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• v.32 no.4
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• pp.535-542
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• 2005

A data broadcast is an efficient technique to deliver data to a number of clients in wireless computing environments. In data broadcast systems, which generally have a narrow bandwidth, a caching is introduced to reduce contention for the bandwidth so that the response time can be decreased. In this paper, unlike previous works that use information maintained by clients, we propose several caching strategies using information on data requests of clients maintained by a server. Then, we evaluate the performance of proposed strategies by using simulation approach. According to the results, the strategy that considers both popularity and waiting time maintained by a server generally shows better performance than other strategies.

• Journal of KIISE:Databases
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• v.32 no.4
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• pp.416-428
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• 2005

In the paper we propose an index method for XML streaming services, where a server broadcasts XML data to a lot of clients in wireless information systems. In order to control the access and tuning time of mobile clients, the proposed method constructs the XML stream through replicating partial index intermixed with parts of data. For this purpose, we propose a two-level tree structure for separating index and XML data into two parts: replicated vs. non-replicated. We analyze the performance of the proposed method with respect to access time and tuning time. With the analysis result, we derive the optimal level value.

• Journal of KIISE:Databases
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• v.33 no.1
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• pp.117-128
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• 2006

In this paper, we propose a streaming method for XML data that supports energy-efficient processing of queries over the stream in mobile clients. We propose new stream organizations for XML data which have different kinds of addresses to related data in a stream. We describe event-driven stream generation algorithms for the proposed stream structures and provide search algorithms for simple XML path queries which leverage the access mechanisms incorporated in the stream. Experimental results show that our approaches can effectively improve the tuning time performance of user queries in a wireless broadcasting environment.

• Journal of KIISE:Databases
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• v.36 no.1
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• pp.30-43
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• 2009

Broadcast in the wireless environment has drawn much attention because it is capable of sending data to clients regardless of the number of clients. Most previous researches have aimed at obtaining an independent data item in a minimum time. But, they have not been researched on simultaneously receiving dependent data items in a query. In addition, these papers have only researched allocation problem that have not been came out data items in a query in same time and different channels. The access probability of each data item based on query request probability have not been reflected. This paper proposes a new method of allocating data items and simultaneously minimizing average response time required in receiving all the dependent data items in a query. Our performance analysis shows that our proposed method gives better average response time over the existing methods.