• 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:Databases
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• v.33 no.1
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• pp.86-101
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• 2006

The bandwidth of channel and the power of the mobile devices are limited on a wireless environment. In this case, data broadcast has become an excellent technique for efficient data dissemination. A significant amount of researches have been done on generating an efficient broadcast program of a set of data items with different access frequencies over multiple wireless broadcast channels as well as single wireless broadcast channel. In this paper, an efficient data allocation method over multiple wireless broadcasting channels is explored. In the traditional approaches, a set of data items are partitioned into a number of channel based on their access probabilities. However, these approaches ignore a variation of access probabilities of data items allocated in each channel. In practice, it is difficult to have many broadcast channels and thus each channel need to broadcast many data items. Therefore, if a set of data items broadcast in each channel have different repetition frequencies based on their access frequencies, it will give much better performance than the traditional approaches. In this paper, we propose an adaptive data allocation technique based on data access probabilities over multiple broadcast channels. Our proposed technique allows the adaptation of repetition frequency of each data item within each channel by taking its access probabilities into at count.

• 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.

• Journal of KIISE:Databases
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• v.32 no.1
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• pp.71-85
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• 2005

Various researches on moving object modeling, uncertainty processing, and moving object indexing have been tarried out in the field of moving object databases. However. previous location tracking systems cannot efficiently retrieve location data of vehicles, because they manage all location information of vehicles using the conventional database. In this paper, we design the vehicle location management systen that is able to manage and retrieve vehicle locations efficiently in mobile environment. The proposed system consists of a server for managing vehicle locations and mobile clients. The system is able to not only process spatiotemporal queries related to locations of moving vehicles but also Provide moving vehicles' locations which are not stored in the system. The system is also able to manage vehicle location data effectively using a moving object index.

• Journal of KIISE:Databases
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• v.35 no.2
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• pp.182-191
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• 2008

Most of previous works for skyline queries have focused only on static attributes of target objects. With the advance in mobile applications, however, the need of continuous skyline queries for moving objects has been increasing. Even though several techniques to process continuous skyline queries have been proposed recently, they cannot process subspace queries, which use only the subset of attribute dimensions. Therefore it is not feasible to utilize those methods for mobile applications which must consider moving objects and subspaces simultaneously. In this paper, we propose a dominant object-based pruning method to compute subspace skyline of moving objects efficiently at query time and present the experimental results to show the effectiveness of the proposed method.

• Journal of Korea Spatial Information System Society
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• v.6 no.1 s.11
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• pp.73-85
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• 2004

Recently, as the growth of the wireless Internet, PDA and HPC, the focus of research and development related with GIS(Geographic Information System) has been changed to the Real-Time Mobile GIS to service LBS. To offer LBS efficiently, there must be the Real-Time GIS platform that can deal with dynamic status of moving objects and a location index which can deal with the characteristics of location data. Location data can use the same data type(e.g., point) of GIS, but the management of location data is very different. Therefore, in this paper, we studied the Real-Time Mobile GIS using the HBR-tree to manage mass of location data efficiently. The Real-Time Mobile GIS which is developed in this paper consists of the HBR-tree and the Real-Time GIS Platform HBR-tree. we proposed in this paper, is a combined index type of the R-tree and the spatial hash Although location data are updated frequently, update operations are done within the same hash table in the HBR-tree, so it costs less than other tree-based indexes Since the HBR-tree uses the same search mechanism of the R-tree, it is possible to search location data quickly. The Real-Time GIS platform consists of a Real-Time GIS engine that is extended from a main memory database system. a middleware which can transfer spatial, aspatial data to clients and receive location data from clients, and a mobile client which operates on the mobile devices. Especially, this paper described the performance evaluation conducted with practical tests if the HBR-tree and the Real-Time GIS engine respectively.

• Proceedings of the Korea Database Society Conference
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• 2001.11a
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• pp.567-581
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• 2001

인터넷이 일반화된 지 불과 10년이 못되었지만, 기업뿐만 아니라 우리 사회 전반에 걸친 패러다임을 변화시키고 있다. 이와 같이 무선인터넷을 기반으로 한 모바일 비즈니스에 대한 관심은 높지만, 기존의 문헌들은 무선인터넷 서비스 수요, 사용자 만족도 등에 관한 연구가 주를 이루고 있다. 즉 모바일 비즈니스 모델을 통한 무선인터넷 서비스의 향후 진화방향에 관한 연구는 전무한 실정이다. 본 연구의 목적은 문헌고찰을 통하여 모바일 비즈니스의 모델들을 정리하고, 오재인(2000)의 The 2$\times$2 Matrix를 분석 툴을 활용하여 모바일 서비스별 현재 수요와 향후 수요를 분석함으로써 모바일 비즈니스의 진화방향을 실증적으로 규명하는 것이다. 1540명의 회수된 설문지 중 유효표본 786개를 대상으로 통계분석을 실시하여 분석된 주요 연구결과는 다음과 같다. 첫째, 모바일 서비스들을 The 2$\times$2 Matrix상에 매핑한 결과 예측에는 별다른 차이가 없는 것으로 나타났다. 둘째, 전체응답자, 사용자, 비사용자들의 모바일 서비스에 대한 순위는 The 2$\times$2 Matrix에서 Mobile Hub, Mobile Trade, Mobile Care, Mobile Support 순으로 나타났다. 셋째, 현재와 향후 각 서비스들 간에는 차이가 있고, 현재 모바일 서비스들 각각과 향후 모바일 서비스들 각각에 대하여 서비스들 순위에는 차이가 없는 것으로 나타났다. 넷째, 무선인터넷의 전반적인 만족도에 영향을 미치는 요인은 우수하고 독특한 컨텐츠, 패킷 과금으로 저렴한 서비스를 제공하는 Cost전략 등으로 나타났다.

• Proceedings of the Korea Database Society Conference
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• 2010.06a
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• pp.267-275
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• 2010

최근 모바일 기술이 지속적으로 발전해 감에 따라 모바일 통신 네트워크를 통한 방송서비스인 모바일 TV가 급속한 확산을 보이고 있다. 기존 모바일 TV 서비스를 대상으로 수행한 선행연구는 주로 모바일 TV 서비스 관련 기술 탐색, 최신 시장동향 분석, 서비스 수용 영향요인 등을 중심으로 연구가 활발히 진행되어 온 반면 서비스 수용 후 행동에 관하여 체계적인 분석을 수행한 연구는 부족한 것이 현실이다. 이러한 배경 하에서, 본 연구는 모바일 TV 서비스 이용자를 대상으로 해당 서비스에 대한 지속적 이용의도 형성에 중요한 영향을 미칠 것으로 예상되는 요인을 파악해 보는 것을 주목적으로 하였다. 연구목적을 효과적으로 달성하기 위하여 본 연구에서는 관련 문헌에 관한 종합적 고찰을 통해 모바일 TV 서비스의 채택 후 행동을 체계적으로 파악해 보기 위하여 지각된 놀이성, 기대 일치, 지각된 사용용이성, 지각된 유용성, 만족, 지속 이용 의도 등 여섯 가지 차원을 포함한 연구모델을 제안하였다. 그리고 제안된 연구모델에 포함된 각 요인들 간의 영향관계에 관한 연구가설을 수립하였다. 향후 모바일 TV 이용자를 대상으로 설문조사를 수행하고, 제안된 모델 및 가설에 대한 실증적 분석을 실시해 보고자 한다. 본 연구의 결과를 토대로 최근 사용자 수가 급증하고 있으며, 높은 관심의 대상이 되고 있는 모바일 TV 분야의 연구자 및 실무자들에게 서비스 이용자를 장기적으로 유지하고, 이를 토대로 지속적인 수익을 창출하는데 도움을 줄 수 있는 시사점을 제공해 보고자 한다.

• Journal of Korea Spatial Information System Society
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• v.6 no.2 s.12
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• pp.23-37
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• 2004

Location Based Services(LBSs) in mobile environments become very popular recently. For efficient LBSs, spatial database management systems must need a spatial indexing scheme such as R-trees in order to manage the huge spatial database. However, it may need unnecessary disk accesses since it needs to access objects which are not actually concerned to user's location-based queries. In this paper, to support the location-based queries efficiently, we propose a CLR-tree(Cell Leveling R-tree) in which a dynamic cell is built up within the minimum bounding rectangle of R-trees' node. The cell level of nodes is compared with the query's cell level in location-based query processing and determines the minimum search space. Also, we propose the insertion, split, deletion, and search algorithms for CRL-trees. From the experimental results, we see that a CLR-tree is able to decrease $5{\sim}20%$ of disk accesses from those of R-trees. So, a CLR-tree can be used for fast accessing spatial objects to user's location-based queries in LBSs.

• Journal of KIISE:Databases
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• v.34 no.3
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• pp.217-231
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• 2007

Frequent disconnection is connected directly to client's cache consistency problem in Mobile Computing environment. For solving cache consistency problem, research about Invalidation Report is studied. But, existent invalidation report structure comes with increase of size of invalidation report structure and decline of cache efficiency if quantity of data become much, or quantity of updated data increases. Also, while existent method confirms whole cache, invalidation report doesn't support selective listening. This paper proposes TTCI(Timestamp Tree-based Cache Invalidation scheme) as invalidation report structure that solve problem of these existing schemes and improve efficiency. We can make TTCI using timestamp of updated data, composing timestamp tree and list ID of data in updated order. If we utilize this, each client can confirm correct information in point that become own disconnecting and increase cache utilization ratio. Also, we can pare down client's resources consumption by selective listening using tree structure. We experimented in comparison with DRCI(Dual-Report Cache Invalidation) that is existent techniques to verify such efficiency of TTCI scheme.