• Journal of Computing Science and Engineering
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• v.4 no.2
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• pp.173-187
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• 2010

Recent technological advances in mobile communication systems have made explosive growth in the number of mobile device users worldwide. One of the most important issues in designing a mobile computing system is location management of users. The hierarchical systems had been proposed to solve the scalability problem in location management. The scalability problem occurs when there are too many users for a mobile system to handle, as the system is likely to react slow or even get down due to late updates of the location databases. In this paper, we propose a top-down clustering algorithm for hierarchical location database systems in a wireless network. A hierarchical location database system employs a tree structure. The proposed algorithm uses a top-down approach and utilizes the number of visits to each cell made by the users along with the movement information between a pair of adjacent cells. We then present a modified algorithm by incorporating the exhaustive method when there remain a few levels of the tree to be processed. We also propose a capacity constraint top-down clustering algorithm for more realistic environments where a database has a capacity limit. By the capacity of a database we mean the maximum number of mobile device users in the cells that can be handled by the database. This algorithm reduces a number of databases used for the system and improves the update performance. The experimental results show that the proposed, top-down, modified top-down, and capacity constraint top-down clustering algorithms reduce the update cost by 17.0%, 18.0%, 24.1%, the update time by about 43.0%, 39.0%, 42.3%, respectively. The capacity constraint algorithm reduces the average number of databases used for the system by 23.9% over other algorithms.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.21 no.2
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• pp.333-338
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• 2017

Recently, because of the mobile device generalization tendency, a lot of new mobile applications which need mobile database on mobile devices appear. SQLite, Realm, etc. are representative mobile databases, and they are the database engines which are suitable for small devices that have large resource restriction and are used a lot in mobile devices based on Linux. These engines are open source programs and have advantages which are lighter weight and faster speed than general purpose databases. This paper focuses on the performance experiments and analysis of SQLite, which is front runner in mobile database fields. Considering the target mobile environments, the test is performed at Linux environment. And this paper implements performance test program and performs performance experiment of SQLite database to test search efficiency. The experiment is processed by comparison with the results of a Oracle database working out at the same environment.

• Journal of the Korea Society for Simulation
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• v.12 no.2
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• pp.55-62
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• 2003

The explosive Increase of wireless networks and the advancement of mobile devices lead to the expansion of mobile environment. In accordance with the development of mobile environment, the need to use mobile database is increased sharply, and also it accompanies the related problems. The current mobile database system is based on the centralized method from which a synchronized server manages multiple mobile database management system to synchronize. From this mobile system architecture, several kinds of problems can be detected such as the management of synchronization issues between mobile databases and the transaction management issues. Furthermore, the current mobile database management system does not consider any solution on the fault tolerance. To solve those problems, this paper proposes the mobile agent-based mobile database management system. The proposed system provide high confidence and efficiency by enhancing the network efficiency and fault tolerance through the mobile grouping.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.24 no.9
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• pp.1117-1122
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• 2020

The improving performance and utilizing application fields of mobile devices are getting bigger and wider. With this trend, applications that use database engines on mobile devices are also becoming common. Applications requiring mobile databases include mobile server databases, edge computing, fog computing, and the like. By the way, the most representative and widely used mobile database is SQLite3. In this paper, we test and compare the update performance of SQLite3 by some file systems. The update performance of the file systems in the mobile environment is an important performance factor in the limited H/W environment. The comparison file system was chosen as FAT, Ext2, and NTFS. Under the same conditions, experiments with each file system to test update performance and characteristics were processed. From the experimental results, we could analyze the advantages and disadvantages of each file system for each database update pattern.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2017.05a
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• pp.109-110
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• 2017

모바일 디바이스들의 사용 보편화와 대용량화로 인해 모바일 환경에 적합한 데이터베이스 엔진들이 최근 다양한 목적으로 모바일 기기에 많이 도입되고 있다. 이 엔진들은 대부분 오픈소스 프로그램들이며 범용 데이터베이스에 비해 가볍고 속도가 빠른 장점을 지녀 향후 발전 가능성이 커보인다. 이 논문에서는 안드로이드 등의 모바일 환경에서 대표적으로 활용되고 있는 SQLite 데이터베이스와 Realm 데이터베이스를 선정하여 검색 성능 및 특성을 파악하고 비교하기 위한 성능 실험을 설계한다.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2003.05a
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• pp.481-484
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• 2003

For map services in the mobile environment, it should be considered that resource restriction of the mobile device. Thus, if a map database dedicated to mobile services may not be developed, the spatial data extracted from general map databases should be simplified before transmitting. This paper suggests the mechanism to simplify and modify the spatial data, which are changed to be able to displayed on the mobile devices. This mechanism is based on the map generalization operations and is refined to adapt on mobile phone environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1612-1616
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• 2006

For map services in the mobile environment, it should be considered that resource restriction or the mobile device. on, if a map database dedicated to mobile services may not be developed, the spatial data extracted from general map databases should be simplified before transmitting. % is paper suggests the filtering methods to manipulate the spatial data, which are changed to be able to displayed on the mobile devices. The suggested methods are evaluated by experiments. This method is based on the map generalization operator 'selection' and is refined to adapt on mobile phone environments.

• Journal of KIISE:Databases
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• v.33 no.1
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• pp.69-85
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• 2006

Broadcast has been often used to disseminate the frequently requested data efficiently to a large volume of mobile clients over a single or multiple channels. Conventional concurrency control protocols for mobile transactions are not suitable for the wireless broadcast environments due to the limited bandwidth of the up-link communication channel. In wireless broadcast environments, the server often broadcast different data items with different frequency to incorporate the data access patterns of mobile transactions. The previously proposed concurrency control protocols for mobile transactions in wireless broadcast environments are focused on the mobile transactions with uniform data access patterns. However, these protocols perform poorly when the data access pattern of update mobile transaction are not uniform but skewed. The update mobile transactions with skewed data access patterns will be frequently aborted and restarted due 4o the update conflict of the same data items with a high access frequency. In this paper, we propose an energy-efficient concurrence control protocol for mobile transactions with skewed data access as well as uniform data access patterns. Our protocol use a random back-off technique to avoid the frequent abort and restart of update mobile transactions. We present in-depth experimental analysis of our method by comparing it with existing concurrency control protocols. Our performance analysis show that it significantly decrease the average response time, the amount of upstream and downstream bandwidth usage over existing protocols.

• Journal of Computing Science and Engineering
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• v.5 no.3
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• pp.210-222
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• 2011

In this work, we study the problem of privacy-preservation data publishing in moving objects databases. In particular, the trajectory of a mobile user in a plane is no longer a polyline in a two-dimensional space, instead it is a two-dimensional surface of fixed width $2A_{min}$, where $A_{min}$ defines the semi-diameter of the minimum spatial circular extent that must replace the real location of the mobile user on the XY-plane, in the anonymized (kNN) request. The desired anonymity is not achieved and the entire system becomes vulnerable to attackers, since a malicious attacker can observe that during the time, many of the neighbors' ids change, except for a small number of users. Thus, we reinforce the privacy model by clustering the mobile users according to their motion patterns in (u, ${\theta}$) plane, where u and ${\theta}$ define the velocity measure and the motion direction (angle) respectively. In this case, the anonymized (kNN) request looks up neighbors, who belong to the same cluster with the mobile requester in (u, ${\theta}$) space: Thus, we know that the trajectory of the k-anonymous mobile user is within this surface, but we do not know exactly where. We transform the surface's boundary poly-lines to dual points and we focus on the information distortion introduced by this space translation. We develop a set of efficient spatiotemporal access methods and we experimentally measure the impact of information distortion by comparing the performance results of the same spatiotemporal range queries executed on the original database and on the anonymized one.

• Journal of Information Technology Services
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• v.8 no.2
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• pp.157-171
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• 2009

In mobile XML environments, the efficient synchronization technique is required to maintain the consistency of replicated XML data because the same data can be replicated between so many different XML documents. In this paper, we propose a message digest based synchronization technique to maintain the consistency of replicated data between client XML documents and a server XML database in mobile XML environments. The proposed an XML data synchronization technique(XSA) has the advantage of model generality aspect and storage space aspect by using the tuple-based message digest table to detect the data conflicts. The proposed technique can be applicable to the application requiring the consistency of replicated XML data without any restrictions in the heterogeneous(between hierarchical XML documents and relational XML databases) mobile environments.