• Journal of KIISE:Computer Systems and Theory
• /
• v.36 no.4
• /
• pp.259-273
• /
• 2009

Most of large-scale distributed file systems decouple a metadata operation from read and write operations for a file. In the distributed file systems, a certain server named a metadata server (MDS) maintains metadata information in file system such as access information for a file, the position of a file in the repository, the namespace of the file system, and so on. But, the existing systems used restrictive metadata management schemes, because most of the distributed file systems designed to focus on the distributed management and the input/output performance of data rather than the metadata. Therefore, in the existing systems, the metadata throughput and expandability of the metadata server are limited. In this paper, we propose a new non-shared metadata management scheme in order to provide the high metadata throughput and scalability for a cluster of MDSs. First, we derive a dictionary partitioning scheme as a new metadata distribution technique. Then, we present a load balancing technique based on the distribution technique. It is shown through various experiments that our scheme outperforms existing metadata management schemes in terms of scalability and load balancing.

• Proceedings of the Korean Information Science Society Conference
• /
• 2003.10b
• /
• pp.34-36
• /
• 2003

최근 들어 위치정보 시스템(GIS)의 발전으로 움직이는 물체의 위치는 쉽게 알 수 있게 되어서 이를 기반으로 미래의 최근접 쌍을 찾는 질의가 중요하게 되었다. 하지만 이동객체는 계속해서 움직이므로 현재의 질의 결과는 시간이 흐름에 따라 유효하지 않게 된다. 본 논문에서는 사용자에게 현재의 가장 인접한 쌍과 이 인접한 쌍이 유효한 시간, 그리고 그 유효한 시간 후에 바뀐 결과를 알려주는 질의를 효율적으로 처리할 수 있는 알고리즘을 제안한다.

• Journal of Korean Society for Geospatial Information Science
• /
• v.4 no.1 s.6
• /
• pp.43-55
• /
• 1996

The objective of this research is to design a digital map database structure supporting video images which is one of the fundamental elements of hypermap. In order to reach the research objective, the work includes the identification of the relationships between two dimensional digital map database and video elements. The proposed database model has functions for interactive browsing between video image frames and specific points on two dimensional digital map, fer connecting the map elements and features on video images. After that, the images and the database are transformed to the pilot system fer testing the map database structure. The pilot project results indicate that the map database structure can integrate functionally two dimensional digital map and video images.

• Journal of KIISE:Databases
• /
• v.35 no.3
• /
• pp.272-285
• /
• 2008

In this paper, we concentrate on data allocation methods for multiple broadcast channels. When the server broadcasts data, the important issue is to let mobile clients access requested data rapidly. Previous works first sorted data by their access probabilities and allocate the sorted data to the multiple channels by partitioning them into multiple channels. However, they do not reflect the difference of access probabilities among data allocated in the same channel. This paper proposes ZGMD allocation method. ZGMD allocates data item on multiple channels so that the difference of access probability in the same channel is maximized. ZGMD allocates sorted data to each channels and applies Broadcast Disk in each channel. ZGMD requires a proper indexing scheme for the performance improvement. This is because in ZGMD method each channel got allocated both hot and cold data. As a result, the sequential search heuristic does not allow the mobile client to access hot data items quickly. The proposed index scheme is based on using dedicated index channels in order to search the data channel where the requested data is. We show that our method achieve the near-optimal performance in terms of the average access time and significantly outperforms the existing methods.

• Proceedings of the Korea Database Society Conference
• /
• 2001.11a
• /
• pp.239-256
• /
• 2001

1. 일관성 (Consistency)과 표준화(Standardization) 2. 유용한 피드백의 제공 3 실수에 대한 대응책(Easy Error Handling) 4. 자기 위치정보의 제공(Internal Locus of Control) 5. 단기 기억부담의 최소화(Minimal Memory Load) (중략)

• Journal of Korea Spatial Information System Society
• /
• v.11 no.1
• /
• pp.43-54
• /
• 2009

As R&D(Research and Development) is going on actively to develop technologies for the ubiquitous computing environment, which Is the human-oriented future computing environment, GIS dealing with spatio-temporal data is emerging as a promising technology. This also increases the necessity of the middleware for providing services to give interoperability in various heterogeneous environments. The core technologies of the middleware are real-time processing technology of data streams coming unceasingly from positioning systems and data stream processing technology developed for non-spatio-temporal data. However, it has problems in processing queries on spatio-temporal data efficiently. Accordingly, this paper designed and implemented the spatio-temporal middleware that provides interoperability between a mobile spatio-temporal DBMS(DataBase Management System) and a server spatio-temporal MMDBMS(Main Memory DataBase Management System). The spatio-temporal middleware maintains interoperability among heterogeneous devices and guarantees data integrity in query processing through real-time processing of unceasing spatio-temporal data streams and two way synchronization of spatio-temporal DBMSs. In addition, it manages session for the connection of each spatio-temporal DBMS and manages resources for its stable operation. Finally, this paper proved the usability of the spatio-temporal middleware by applying it to a real-time position tracking system.

• Journal of KIISE:Databases
• /
• v.33 no.3
• /
• pp.299-309
• /
• 2006

Due to the rapid development in mobile communication technologies, the usage of mobile devices such as cell phone or PDA becomes increasingly popular. As different devices require different applications, various new services are being developed to satisfy the needs. One of the popular services under heavy demand is the Location-based Service (LBS) that exploits the spatial information of moving objects per temporal changes. In order to support LBS efficiently, it is necessary to be able to index and query well a large amount of spatio-temporal information of moving objects. Therefore, in this paper, we investigate how such location information of moving objects can be efficiently stored and indexed. In particular, we propose a novel location encoding method based on hierarchical administrative district information. Our proposal is different from conventional approaches where moving objects are often expressed as geometric points in two dimensional space, (x,y). Instead, in ours, moving objects are encoded as one dimensional points by both administrative district as well as road information. Our method is especially useful for monitoring traffic situation or tracing location of moving objects through approximate spatial queries.

• Journal of KIISE:Information Networking
• /
• v.35 no.1
• /
• pp.76-90
• /
• 2008

Wireless sensor networks are expected to play a vital role in the upcoming age of ubiquitous computing such as home environmental, industrial, and military applications. Compared with the vivid utilization of the sensor networks, however, security and privacy issues of the sensor networks are still in their infancy because unique challenges of the sensor networks make it difficult to adopt conventional security policies. Especially, node compromise is a critical threat because a compromised node can drain out the finite amount of energy resources in battery-powered sensor networks by launching various insider attacks such as a false data injection. Even cryptographic authentication mechanisms and key management schemes cannot suggest solutions for the real root of the insider attack from a compromised node. In this paper, we propose a novel trust-based secure aggregation scheme which identifies trustworthiness of sensor nodes and filters out false data of compromised nodes to make resilient sensor networks. The proposed scheme suggests a defensible approach against the insider attack beyond conventional cryptographic solutions. The analysis and simulation results show that our aggregation scheme using trust evaluation is more resilient alternative to median.

• Journal of KIISE:Information Networking
• /
• v.32 no.1
• /
• pp.80-88
• /
• 2005

In ubiquitous spaces, a user wants to be provided with a VOD service while moving one space to another freely. Since the traditional VOD system is dependent on user location, the VOD server transmits video data to a single client during a session. If the user moves to another space, he/she should close the old session and make a new request for the same video. However, the location-aware VOD system supports user mobility by closing and opening the session automatically. That is, the VOD system automatically perceives the movement of a user and allows the server to change the data flow so that a client near the user can receive the video data. This paper proposes a location-aware VOD service architecture and a session handoff scheme to provide a mobile user with continuous video delivery and implements a location-aware VOD prototype system based on Jini and Java. In experiment, we show that the proposed handoff scheme has a smaller handoff delay than the other handoff scheme.

• Proceedings of the Korean Information Science Society Conference
• /
• 2005.11b
• /
• pp.52-54
• /
• 2005

시퀀스 데이타는 크기를 가지는 일련의 값들로 이루어져 있어 일반적인 상품 데이타와는 달리 서로간의 관계성을 파악하기가 어려운 것으로 알려져 있다. 본 논문에서는 이러한 문제점을 해결하기 위하여 관계성을 보이는 시퀀스를 유사 시퀀스로 검색해 내는 기법을 제안한다. 이를 위해 유클리드 거리만으로 유사도가 결정되던 기존의 유사 검색을 변형하여 시퀀스의 상대적 위치와 형태를 고려한 시퀀스의 변화율을 척도로 사용하였으며 고차원이라는 문제를 해결하기 위하여 관계성을 수치로 표현하였다. 또한 본 논문에서는 기존의 하르 웨이블릿을 변형한 기하 웨이블릿을 이용하여 인덱스를 구성하였으며 보정 과정을 통해 기존의 유사 검색 기법으로도 문제가 변형될 수 있음을 보였다.