Jin-Tak Choi

Ontology-based composition of web services for ubiquitous computing

Current Web service environment provide connection to individual services but is still deficient in semantic processing technology for the interoperability of Web services. The semantic processing of Web services is a key technology for the dynamic discovery and composition of Web services. Thus, the present study established Web service ontology to support ubiquitous environment and proposed a method of describing Web services in consideration of their functional and semantic aspects. In addition, it implemented a service interlocking and composition system by including a mediator function, which enables the composition of heterogeneous Web services, in the system.

A Distributed Air Index Based on Maximum Boundary Rectangle over Grid-Cells for Wireless Non-Flat Spatial Data Broadcast

In the pervasive computing environment using smart devices equipped with various sensors, a wireless data broadcasting system for spatial data items is a natural way to efficiently provide a location dependent information service, regardless of the number of clients. A non-flat wireless broadcast system can support the clients in accessing quickly their preferred data items by disseminating the preferred data items more frequently than regular data on the wireless channel. To efficiently support the processing of spatial window queries in a non-flat wireless data broadcasting system, we propose a distributed air index based on a maximum boundary rectangle (MaxBR) over grid-cells (abbreviated DAIM), which uses MaxBRs for filtering out hot data items on the wireless channel. Unlike the existing index that repeats regular data items in close proximity to hot items at same frequency as hot data items in a broadcast cycle, DAIM makes it possible to repeat only hot data items in a cycle and reduces the length of the broadcast cycle. Consequently, DAIM helps the clients access the desired items quickly, improves the access time, and reduces energy consumption. In addition, a MaxBR helps the clients decide whether they have to access regular data items or not. Simulation studies show the proposed DAIM outperforms existing schemes with respect to the access time and energy consumption.

A Multi-level Grid-Based Air Indexing Scheme for Window Query Processing in Wireless Data Broadcast Environments

Air indexing schemes of spatial data items have been researched for effective processing of spatial queries. However, the schemes cause the mobile clients to wait long for their desired items and to consume energy much. In this paper, we propose a new indexing scheme based on multi-leveled grid for window query processing on air. It allows fast and energy efficient processing of window query. Also, it has a linear structure matching the linear access pattern of the clients and makes them access only the queried data items. The simulations show that the proposed scheme outperforms the existing schemes in terms of access latency and energy efficiency.

New distributive web-caching technique for VOD services

At present, one of the most popular services through internet is on-demand services including VOD, EOD and NOD. But the main problems for on-demand service are excessive load of server and insufficiency of network resources. Therefore the service providers require a powerful expensive server and clients are faced with long end-to-end delay and network congestion problem. This paper presents a new distributive web-caching technique for fluent VOD services using distributed proxies in Head-end-Network (HNET). The HNET consists of a Switching-Agent (SA) as a control node, some Head-end Nodes (HEN) as proxies and clients connected to HEN. And each HEN is composing a LAN. Clients request VOD services to server through a HEN and SA. The SA operates the heart of HNET, all the operations using proposed distributive caching technique perform under the control of SA. This technique stores some parts of a requested video on the corresponding HENs when clients connected to each HEN request an identical video. Thus, clients access those HENs (proxies) alternatively for acquiring video streams. Eventually, this fact leads to equi-loaded proxy (HEN). We adopt the cache replacement strategy using the combination of LRU, LFU, remove streams from other HEN prior to server streams and the method of replacing the first block of video last to reduce end-to end delay.