• 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.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:Computing Practices and Letters
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• v.12 no.5
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• pp.300-311
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• 2006

Traffic information is considered as one of the core contents of the terrestrial DMB. This paper proposes and implements the data broadcasting system, which automatically collects data and transmits the contents in order to provide traffic information promptly The proposed data broadcasting system comprises the following three subsystems: 1 he traffic information integration system for collecting and processing data in real-time, the traffic information authoring system for automatically creating and verifying the contents, and the traffic information transmission system for transmitting the created contents. We describe these subsystems in detail about their functionality, components and interoperability. The proposed data broadcasting system provides the HWS type contents as the PAD data of the terrestrial DMB audio broadcast. Finally, we describe our implementation of the data broadcasting system, and suggest further improvements that need to be made.

• Journal of KIISE:Databases
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• v.30 no.6
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• pp.561-572
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• 2003

Broadcast-based data delivery has attracted a lot of attention as an efficient way of disseminating data to very large client populations. The main motivation of broadcast-based information systems (BBISs) is that the number of clients that they serve can grow arbitrarily large without any effect on their performance. The performance of BBISs depends mainly on client caching strategies and on data broadcast scheduling mechanisms. This paper addresses the former issue and proposes a new client cache management scheme, named 2Q-CFP, that is suitable to BBISs. This paper also evaluates the performance of 2Q-CFP on the basis of a simulation model. The performance results indicate that 2Q-CFP scheme shows superior performances over GRAY, LRU and CF in the average response time.

• 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.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.28 no.4
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• pp.715-722
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• 2001

Mobile computing has become a reality thank to the convergence of two technologies :powerful portable computers and the wireless networks. The restrictions of wireless network such as bandwidth and energy limitations make data broadcasting an attractive data communication method. This paper addresses the clustering of wireless broadcast data for multipoint queries. By effective clustering of broadcast data the mobile client can access the data on the air in short latency In the paper we define the data affinity and segment affinity measures. The data affinity is the degree that two data objects are accessed by queries, and the segment affinity is the degree that two sets of data (i.e segments) are accessed by queries Our method clusters data objects based on data and segment affinity measures we show that the performance of our method is scarcely infuenced by the growth of the number of queries.

• Broadcasting and Media Magazine
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• v.8 no.2
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• pp.58-67
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• 2003

• 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.