Masahiko Tsukamoto

Dot: A term representation using dot algebra for knowledge-bases

This paper proposes a knowledge representation DOT (Deductive and Objectoriented Term representation), which employs extended terms to describe the properties of objects using dot notation and IS-A relation. Its semantics is provided on a quasi-ordering structure called DOT algebra. DOT presents a simple framework for inheritance and becomes an inference engine for knowledge-bases constructed from the IS-A relation. We discuss how to resolve three fundamental problems of DOT algebra, and demonstrate that a class of queries called bounded query can be evaluated by those resolution methods, in which a regular expression of automata theory assumes a central role.

Image-Based Pseudo-3D Visualization of Real Space on WWW

The conventional approaches for constructing real-space-based 3D space on WWW are costly much in initial modeling and in network access in its operation. The recent trend in such construction, i.e., the image-based rendering (IBR) approach, focuses on more convenient handling of the real space, but the obtained space is usually constrained by the difficulty in image analysis. In this paper, aiming at relaxing the modeling cost of the real space and the accessing cost on WWW, we propose a simple approach where we use scenic images such as those taken by a digital camera or a video camera without distorting them. By enlarging or shrinking an avatar image and pasting it on a background scenic image according to the users input, we can visualize the depth of the scene as pseudo 3D space. We call the method the image-based nonrendering (IBNR), intended as an antithesis to IBR. In our system, we emphasize on two points: the scene independency, i.e., each scene is more independent of other scenes, and the platform independency, i.e., usual WWW browsers can be used in the walk-through of the space without extra plug-ins.

Database migration: a new architecture for transaction processing in broadband networks

Due to recent developments in network technologies, broader channel bandwidth is becoming prevalent in worldwide networks. As one of the new technologies making good use of such broadband channels, dynamic relocation of databases through networks, database migration, will soon be used in practice as a powerful and basic database operation. We propose two transaction processing methods to take advantage of database migration in broadband networks. These methods choose the most efficient transaction processing method between the conventional method, based on the two-phase commit protocol, and our method, using database migration. We also propose a concurrency control mechanism and a recovery mechanism for our proposed methods. Simulation results are presented comparing the performance of our proposed methods and the conventional transaction processing method based on the two-phase commit protocol. The results demonstrate that the effective use of database migration produces better performance than the conventional method.

A user customized selection and categorization for broadcast data

Recently, many broadcast satellites have been launched to provide data broadcasting services for public users. Although the provided services can cover many kinds of data and a wide range of user interest, it is considered that, in general, a user is interested in only some specific genres of data. Consequently, storing all received data is considered to be inefficient and only wasting a large amount of memory. This motivated us to introduce an information filtering system into a broadcast data receiving system. The use of filtering system increases the efficiency of memory usage and reduces time for searching interesting data. In this paper, we propose a filtering method that uses a tree structure to represent user preferences. The use of this filtering method enable the receiving system to select only data that match users interest and classify the stored data in the way that suits the users access pattern. We also describe the design and implementation of our broadcast data. Receiving system that makes use of the proposed filtering method. Further, we evaluate the performance of our method by showing some simulation results.

DB-MAN: a distributed database system based on database migration in ATM networks

Because of the recent development of network technologies such as ATM (Asynchronous Transfer Mode), broader channel bandwidth is becoming available everywhere in the world wide networks. As one of the new technologies to make good use of such broadband channel, dynamic relocation of databases through networks, which we call database migration, will soon become a powerful and basic database operation of practical use. We discuss our proposal of a distributed database system, DB-MAN (distributed database system based on DataBase Migration in ATM Networks), which takes advantage of database migration in virtual LANs (local area networks) of ATM networks. DB-MAN has two notable mechanisms: a mechanism for selecting the transaction processing method and a mechanism for concurrency control with database migration. The former, is a mechanism which chooses the more efficient method between two transaction processing methods: the conventional method based on the two phase commit protocol and our method employing database migration. The latter is a mechanism to prevent the transaction processing throughput from deteriorating in environments where data contention is a significant factor. Then we show simulation results regarding performance comparison between our proposed system and the conventional distributed database system based on the two phase commit protocol. The obtained results demonstrate that effective use of database migration gives higher performance than that of the conventional system.

Strategies for Query Processing in Mobile Computing

In this paper, we discuss several strategies for efficient processing of three types of queries concerning mobile hosts; (1) queries to obtain the location of a mobile host (location queries), (2) queries to determine whether the mobile host is currently active (existence queries), and (3) queries to obtain a piece of information from a mobile host (data queries). Extracting five fundamental strategies from those usually employed in mobile communication protocols, we shall discuss their features and then compare their performance. These five strategies are: single broadcast notification (SBN), double broadcast notification (WBN), broadcast query forwarding (BQF), single default notification (SDN), and double default notification (WDN). We show that the optimal strategy varies according to network conditions such as network topology, network scale, migration rate, and query occurrence rate.

Performance comparison of mobile support strategies

This paper presents performance comparison among five strategies for mobile support. The major facilities that are required for a network protocol to support mobile hosts are location management and packet forwarding. Based on this observation, we consider five basic strategies which use distinct methods to achieve these facilities and compare their performance. These five strategies are Broadcast Kotification (BN), Broadcast Forwarding (BF), Broadcast Query (BQ), Default Forwarding (DF), and Default Query (DQ). As a result of analytical evaluation and comparison, it is shown that under different network conditions, such as number of routers, network topology, migration/communication ratio, data/control packet size ratio, different strategies produce minimum network traffic. In short, DF and DQ show the best performance in scalability, while BF and BQ are efficient for frequent migration. On the other hand, BN is suitable for a small network which has hosts with rare migration.

A CLNP-based protocol for mobile end systems within an area

A protocol for supporting mobile end systems (ESs) that move within an area in a connectionless-mode network protocol (CLNP) environment is proposed. Traffic caused by control protocol data units under frequent ES migration can be reduced by separating the roles of intermediate systems (ISs) into two roles: (1) generating and propagating the information of the default location of an ES, and (2) communicating directly to the ES and notifying the IS performing the role (1) of the current location of the ES. In addition, ISs may use a new caching mechanism for efficiency. This protocol has the following advantages: First, there is no need for mobile ESs to be changed. Second, ISs implementing this protocol can coexist with the conventional ISs. Third, it does not require any change to the areas which do not have mobile ESs, so it is easy to apply to the existing networks.<<ETX>>

Main memory database for supporting database migration

As one of the new technologies to make good use of broader channel bandwidth of recent networks, dynamic relocation of databases through networks, which we call database migration, will soon become a powerful and basic database operation of practical use. To make full use of database migration, the main memory database is considered to be one of the most significant technologies, because it allows us to perform very high speed database access which almost matches for the transmission rate of broadband networks. In this paper, we first discuss the physical database structure which realizes high speed database migration. Then, we propose the recovery methods for migratory main memory databases.

Knowledge discovery in deductive databases with large deduction results: the first step

Deductive databases have the ability to deduce new facts from a set of existing facts by using a set of rules. They are also useful in the integration of artificial intelligence and databases. However, when recursive rules are involved, the number of deduced facts can become too large to be practically stored, viewed or analyzed. This seriously hinders the usefulness of deductive databases. In order to overcome this problem, we propose four methods to discover characteristic rules from a large number of deduction results without actually having to store all the deduction results. This paper presents the first step in the application of knowledge discovery techniques to deductive databases with large numbers of deduction results.