• Journal of KIISE:Databases
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• v.32 no.4
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• pp.405-415
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• 2005

Indexing techniques are used to implement selective tuning in wireless environments Indices are broadcast together with data to help mobile clients locate the required information. As a result, clients stay in doze mode most of the time. The drawback of this solution is that broadcast cycles are lengthened due to additional index information. In location-aware mobile services(LAMSs), it is important to reduce the query response time, since a late query response nay contain out-of-date information. In this paper, we present a broadcast-based spatial query processing method (BBS) designed to support k-NN query processing. In the BBS, broadcasted data objects are sorted sequentially based on their locations, and the server broadcasts the location dependent data along with an index segment. The performance of this scheme is investigated in relation to various environmental variables, such as the distributions of the data objects, the average speed of the clients and the size of the service area.

• Journal of KIISE:Databases
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• v.30 no.1
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• pp.95-107
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• 2003

The broadcast environment has asymmetric communication aspect that is typically much greater communication bandwidth available from server to clients than in the opposite direction. In addition, most of mobile computing systems allow mostly read-only transactions from mobile clients for retrieving different types of information such as stock data, traffic information and mews updates. Since previous concurrency control protocols, however, do not consider such a particular characteristics, the performance degradation occurs when previous schemes are applied to the broadcast environment. In this paper, we propose the efficient concurrency control for query transaction in broadcast environment. The following requirements are satisfied by adapting weak consistency that is the appropriate correctness criterion of read-only transactions: (1) the mutual consistency of data maintained by the server and read by clients (2) the currency of data read by clients. We also use the serialization graph scheme to check the weak consistency efficiently. As a result, we improved a performance by reducing unnecessary aborts and restarts of read-only transactions caused when global serializability was adopted.

• Journal of KIISE:Databases
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• v.29 no.6
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• pp.477-491
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• 2002

The broadcast environment has asymmetric communication aspect that is typically much greater communication bandwidth available from server to clients than in the opposite direction. In addition, mobile computing systems generate mostly read-only transactions from mobile clients for retrieving different types of information such as stock data, traffic information and news updates. Since previous concurrency control protocols, however, do not consider such a particular characteristics, the performance degradation occurs when previous schemes are applied to the broadcast environment. In this paper, we propose optimistic concurrency control based on timestamp interval for broadcast environment. The following requirements are satisfied by adapting weak consistency that is the appropriate correctness criterion of read-only transactions: (1) the mutual consistency of data maintained by the server and read by clients (2) the currency of data read by clients. We also adopt the timestamp Interval protocol to check the weak consistency efficiently. As a result, we improved a performance by reducing unnecessary aborts and restarts of read-only transactions caused when global serializability was adopted.

• Journal of Internet Computing and Services
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• v.1 no.1
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• pp.35-46
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• 2000

One of the main chalenges in personal communication services (PCS) is to locate many mobile terminals that may move frequently from place to place. Such a system operation is called location management. Many network signaling traffic, and database queries are required to achieve such a task. Several strategies have been proposed to improve the efficiency of location management. These strategies use location register databases to store the current location on mobile terminals, and are vulnerable to failure of the location registers. In this paper, we propose a fault-tolerant pointer forwarding with distributed home location register (FT-RFDHLR) to tolerate the failure of location registers. The performance of the proposed method is evaluated by an analytical model, and is compared with thew pointer forwarding with the single home location register (PFSHLR), the pointer forwarding with distributed home location register (PFDHLR), Biaz's bypass forwarding strategy (BFS) and two-path forwarding strategy (TPFS).

• Journal of the Korea Institute of Information Security & Cryptology
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• v.30 no.3
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• pp.369-378
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• 2020

Due to the widespread use of mobile devices, smartphone penetration and usage rate continue to increase and there is also an increasing amount of data that need to be stored and managed in applications. Therefore, recent applications use mobile databases to store and manage user data. Realm database, developed in 2014, is attracting more attention from developers because of advantages of continuous updating, high speed, low memory usage, simplicity and readability of the code. It also supports an encryption to provide confidentiality and integrity of personal information stored in the database. However, since the encryption can be used as an anti-forensic technique, it is necessary to analyze the encryption and decryption processes provided by Realm Database. In this paper, we analyze the structure of Realm Database and its encryption and decryption process in detail, and analyze an application that supports an encryption to propose the use cases of the Realm Database.

• Journal of KIISE:Databases
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• v.31 no.4
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• pp.422-431
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• 2004

In recent years, different models in data delivery have been explored in mobile computing systems. Particularly, there were a lot of research efforts in the periodic push model where the server repetitively disseminates information without explicit request. However, average waiting time per data operation highly depends on the length of a broadcast cycle and different access pattern among clients may deteriorate the response time considerably. In this case, clients are preferably willing to send a data request to the server explicitly through backchannel in order to obtain optimal response time. We call the broadcast model supporting backchannel as hybrid broadcast. In this paper, we devise a new transaction processing algorithm(O-PreH) in hybrid broadcast environments. The data objects which the server maintains are divided into Push_Data for periodic broadcasting and Pull_Data for on-demand processing. Clients tune in broadcast channel or demand the data of interests according to the data type. Periodic invalidation reports from the server support maintaining transactional consistency. If one or more conflicts are found, conflict orders are determined not to violate the consistency(pre-reordering) and then the remaining operations have to be executed pessimistically. Through extensive simulations, we demonstrate the improved throughput of the proposed algorithm.

• 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.

• Proceedings of the KSPS conference
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• 2002.11a
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• pp.119-122
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• 2002

This paper focuses on building up a database of commercial stocks using XML syntax and looks into a way of building up a system with the combination of XML and XSLT that provides connectivity to client-server databases through vocal means. The use of XSLT has several advantages. Most importantly, it can transform a type of data into different formats. A vocal interface minimizes some space and time limits imposed on users outside premises when they need an instant connection to their database. In this fashion, the users can check information on stock lists without being pressurized by certain limits. PC, PDAs and cellular phones are some examples of mobile connection. The use of VoiceXML creates vocal applications. In VoiceXML servies, users can gain immediate access to data upon the input of their voices and the DTMF signals of the telephone.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10b
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• pp.93-95
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• 1998

본 논문에서는 기존의 파일 시스템을 이용한 모빌 에이전트가 아나라, 분산된 서로 다른 데이터베이스 환경에서 효과적인 데이터 탐색을 위한 디렉토리와 옐로우 페이지를 모빌 에이전트를 이용하여 설계하고 구현하였다. 그리고 개발 환경은 서로 다른 Windows NT와 유닉스 시스템을 혼용하였고, 플랫폼에 독립적인 Java 언어와 통합 모질 에이전트 환경을 지원하는 ASDK를 사용하였다. 이러한 기능을 전투 상황이라는 시나리오에 적용하였다. 신속하게 여러 부대 가용자산 정보를 수집해야 하는 긴박한 상황 속에서 이미 Traffic Jam 상태에 있는 제한되어있는 통신망은 요구하는 속도를 충족시키기 곤란할 것이다. 이러한 상황 속에서 모빌 에이전트의 활발한 활동은 필요한 데이터를 지속적으로 갱신, 탐색 할 것이며, 특히 모빌 컴퓨팅 환경과 결합되어 더욱 효율적인 결과를 나타낼 것이다.

• Proceedings of the Korean Information Science Society Conference
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• 2011.06c
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• pp.258-261
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• 2011

Living in the age of information people face problems related to information overload. Information is easy to produce, store and distribute through various communication channels, one of which is emails. With the appearance of the mobile devices, such as smart phones and tabs, people can have access to email inbox at any moment of time from everywhere. In this paper we present information extraction system with a specific goal of extracting meeting location from the announcement of seminar or conference. We apply a machine learning method (conditional random fields, CRF), train the system using annotated corpus of seminar and conference announcements and validate results by applying various extracted correction rules and patterns. Furthermore, we normalize extracted location, and reference using geo-coding databases, OpenStreetMap and Wikipedia resources to determine real geographical coordinates.