Miseon Choi

A Context-Based Collaboration System in Ubiquitous Environments

In ubiquitous environments, invisible devices and software are connected to one another to provide convenient services to users. In order to provide such services, we must have mobile devices that connect users and services. However, the types of services available have thus far been limited due to the limited resources of mobile devices. This paper will propose a solution to the resource problem of mobile devices by presenting a context-based collaboration system that allows mobile devices to share various nearby resources. We have tested our context-based collaboration system by using the test scenario. This paper focuses on sharing different devices by recognizing context data in a given situation.

A split synchronizing mobile transaction model

We propose a new notion of hoardset fragmentablilty and SSMT(Split Synchronizing Mobile Transaction) model for ubiquitous mobile clients, which not only assures transaction atomicity in synchronization but also reduces synchronization cost and provides context-awareness in ubiquitous computing environment with uneven conditioning. It splits the synchronization process of a mobile transaction into 2 parts by exploiting the hoardset fragmentability of data objects which the mobile transaction access: preferred and deferred synchronization part. The deferred synchronization part which has no possibility of conflict uses the data-centric synchronization strategy and its synchronization is delayed. The preferred synchronization part with possibility of conflicts is synchronized early using the transaction-centric synchronization strategy. We also propose a new data hoarding and synchronization mechanism which facilitates the split synchronization of SSMT. The performance evaluation model for the SSMT is developed and its results are compared to a conventional transaction-centric synchronization model.

Two-step backup mechanism for real-time main memory database recovery

Proposes a recovery mechanism for real-time main-memory database systems (RT-MMDBSs) which aims at reducing the system recovery time, as well as ensuring a fast response time and predictability. Conventional main-memory database (MMDB) recovery schemes usually use logging with checkpointing, which involves many disk I/Os during transaction processing. Consequently, it not only ensures the predictability of the response time, but also fast recovery, because undo/redo logs should be analyzed and applied after failure. Our recovery mechanism replaces logging and checkpointing activities with a single backup activity, which results in eliminating the need for log writing. Furthermore, it performs transaction processing and backup processing in separate areas, as a result minimizing their interference with each other. We use part of the main memory as a shadow memory area and the stable memory as a backup buffer. In our scheme, a two-step page-based backup is made: the first backup step is done from the shadow memory to the backup buffer, and the second step is performed from the backup buffer to a backup disk. We briefly show the worst-case performance analysis of our mechanism.

Two-phase mobile transaction validation in wireless broadcast environments

In this paper, we propose a two-phase mobile transaction validation protocol making the best use of the strong point of (l, m) indexing broadcast data organization in wireless broadcast environments. It is based on OCC(Optimistic Concurrency Control) protocol which minimizes the excessive bi-directional communication by making transactions execute unhindered to their validation point. In the proposed protocol, the validation of a mobile transaction is performed in two-phase: partial validation phase and final validation phase. The partial validation is performed at the mobile client based on the control information contained in the broadcast disk and the final validation is performed on the committed and active transactions at the server. The proposed protocol tries to minimize the restart rate of mobile transactions as well as average transaction response time through adjusting serialization order of mobile transactions by exploiting the potential read/write set of mobile transactions.

A Hybrid Cache Cohrency Scheme for Ubiquitous Mobile Clients

We propose a new cache coherency scheme named HCCS(hybrid cache coherency scheme) to facilitate ubiquitous data access of mobile clients. To cope with the limitations of ubiquitous computing environments, it integrates the cache invalidation scheme using broadcast channel into the publish/subscribe-based data synchronization scheme using two-way communication channel. We present novel algorithms and system architecture for the HCCS. By integrating two schemes, the HCCS provides substantial benefits: allows updates on the mobile client which are restricted in the cache invalidation scheme using broadcast channel and disconnected operations, improves the scalability. The HCCS scheme also gives proper support to the short disconnection of mobile clients, dynamically adapts to changes of disconnection period of the mobile clients.

Improving real-time interoperation of national defense M&S system using distributed DBMS

As M&S (Modeling and Simulation) systems are developed in National Defense field, demand of sharing and managing simulation data in real-time during simulation is increasing. Simulation data is interchanged as FOM (Federation Object Model) type through the standard interoperation system, HLA/RTI (High Level Architecture / Real-Time Infrastructure). Guaranteeing real-time performance during M&S training is the most important. However, FOM type of interchanging simulation data in HLA/RTI does not ensure real-time management since FOM data is disposable that can be used only once. We suggest adding distributed DBMS to the existing HLA/RTI system to achieve the real-time interoperation of simulation data, and also design RTI-DB (Real-Time Infrastructure - DataBase) Coordinator for effective data interchange between HLA/RTI system and distributed DBMS to support real-time management of simulation data during simulation. This paper will discuss the proposed system as well as the evaluation of its potential performance.

An agent-based personalized multimedia Jukebox for mobile devices using consumption sentiment 2

This paper classifies the users purchase pattern into four types of behavior, and proposes an agent-based personalized multimedia Jukebox that provides a personalized service on the client side. The proposed Jukebox assists the efficient management of numerous multimedia contents stored in a personal desktop computer, and provides personalized multimedia contents to the mobile device based on a push service type.

Dynamically Personalized Music Recommendation System for PDA

We introduce a novel personalized music service system through PDA. By providing only users’ preferred web pages or smaller readable service pages, the problem of the limitation of resource of PDA can be solved. In this paper, the preferred service pages are obtained from the statistical preference transactions among web pages for each web site. In computing the preference, we consider the ratio of the different of time which was visited and users’ real listening time of music recommended. We present a novel algorithm to compute the time weights for different items in a manner that will assign a decreasing weight to old data. Also, our system dynamically provides the personalized music service according to the different three cases such as the beginning stage, the positive feedback, and the negative feedback. In the experimental section, we demonstrate our personalized music service system and show how much the resource of mobile devices can be saved.

A Split Synchronizable Mobile Transaction Processing Model for e-Business Applications in Ubiquitous Computing Environment

An e-business client application in ubiquitous mobile computing environment may become disconnected from the enterprise server due to broken communication connections caused by the limitation of mobile computing environments(limited battery life of the mobile device, low bandwidth communication, incomplete wireless communication infrastructure, etc). It Is even Possible that mobile client application Intentionally operates in disconnected mode to reduce communication cost and the power consumption of the mobile device. We use “data hoarding” as a means of providing local autonomy to allow transactions to be processed and committed on the mobile host despite of disconnection. The key problem to this approach is the synchronization problem that serialize potentially conflicting updates from disconnected clients on master objects of the server database. In this paper, we present a new transaction synchronizing method that splits a transaction into a set of independent component transactions and give the synchronization priority on each component taking the possibility of use and conflicts in the server into consideration. Synchronization is performed component by component based un synchronization priority. After the Preferred component of a no bile transaction succeeds in synchronization with the server, the mobile transaction can pre-commit at server. A pre-committed transaction`s updated value is made visible at server before the final commit of the transaction. The synchronization of the component with low synchronization priority can be delayed in adaption to wireless bandwidth and computing resources. As a result, the availability of important data updated by mobile client is increased and it can maximize the utilization of the limited wireless bandwidth and computing resources.