What Is a Mobile Database?

As an extension and extension of a distributed database, a mobile database has many advantages and unique characteristics of a distributed database. It can meet the requirements for people to access information in the future, and has a broad application prospect.

Chinese name: Mobile database
Architecture: Mobile host mobile support site, fixed host

Key technology: Copy and cache technology
Features: Miniaturized kernel structure

Mobile Database Mobile Database Overview

Mobile database mobile database concept

A mobile database is a database capable of supporting a mobile computing environment. Its data is physically dispersed and logically centralized. It involves multiple disciplines such as database technology, distributed computing technology, and mobile communication technology. Compared with traditional databases, mobile databases have the characteristics of mobility, location correlation, frequent disconnection, and asymmetry of network communication. .

Mobile database mobile database system structure and classification

A typical mobile database prototype system structure is shown in the figure.

Mobile databases can be viewed as an extension of traditional database systems. Mobile database systems are roughly classified as follows:

a. Mobile multi-database system.

b. Mobile homogeneous database system.

c. Mobile heterogeneous database systems.

d. Mobile heterogeneous multi-database system.

Mobile database mobile database architecture

The mobile database basically consists of three types of hosts: Mobile Hosts, Mobile Support Stations, and Fixed Hosts.

A fixed host is a computer in the usual meaning. They are connected through a high-speed fixed network and cannot manage mobile devices. The mobile support site has a wireless communication interface that can communicate with mobile devices for data. The communication between the mobile support site and the fixed host is over a fixed network. The area covered by a mobile support site is called a cell, and a mobile host within a cell can communicate with the mobile support site covering this area through a wireless communication network to complete the retrieval of information data.

The key technology of mobile database

(1) Copy and cache technology. In a mobile database environment, response time is improved by using a weakly consistent server-level replication mechanism. Cache technology is to reduce the frequency of clients accessing the database server by caching part of the data on the data server on the client.

(2) Data broadcasting technology. Using the network asymmetry in which the downstream bandwidth from the server to the mobile client is much larger than the upstream bandwidth from the mobile client to the server, the data frequently accessed by most mobile users is organized and provided to periodic broadcasts. Mobile client.

(3) Location management. The location management of mobile users is mainly focused on two aspects: one is how to determine the current location of the mobile user, and the other is how to store, manage and update location information. A mobile computer can be permanently registered on its own host server, and when it moves to any other area, its host server is notified of its current location.

(4) Query processing and optimization. In the mobile database environment, due to the user's movement, frequent disconnection and the diversity of the network environment in which the user is located, mobile query optimization must adopt a dynamic strategy to adapt to the changing picture environment.

(5) Mobile transaction processing.

The key of mobile database embedded mobile database in application

(1) Data consistency issues. A significant feature of the mobile database is a weak connection between the mobile terminal and the server, that is, low bandwidth, long latency, instability, and frequent disconnection. In order to support users' operations on databases in weak environments, optimistic replication methods are now commonly used, allowing users to operate on data copies on the local cache, after the network is reconnected, exchange data modification information with the database server or other terminals, and Conflict detection mechanism to coordinate and restore data consistency.

(2) Efficient transaction processing. New transaction management strategies and algorithms are designed and implemented by adopting strategies such as a complete logging strategy and real-time updating of user location attributes during transaction movement.

(3) Data security. Authentication of mobile terminals to prevent fraudulent access by illegal terminals; encryption of wireless communications to prevent data leakage; encrypted storage of downloaded data copies to prevent data leakage after physical loss of mobile terminals and other means to ensure data security .

Characteristics of mobile database mobile database management system

(1) Miniaturization of the kernel structure.

(2) Support for standard SQL.

(3) Enhancement of transaction management functions.

(4) Perfect data synchronization mechanism.

(5) Supports multiple connection protocols such as serial communication, TCP / IP communication, infrared, and Bluetooth.

(6) Complete embedded database management functions.

(7) Support a variety of currently popular embedded operating systems such as Windows CE, Palm OS.

Mobile database mobile database data management

(1) Distribution and replication of data. Data is unevenly distributed among base stations and mobile units. A significant feature of the mobile database is that the connection between the mobile terminal and the server is a weak connection, that is, the broadband, long delay, instability and frequent disconnection, which increases due to the constraint of database consistency This makes it difficult to manage the cache. The method commonly used now allows the mobile unit to handle its own transactions and operate on a copy of the data on the local cache. When disconnected for a long time, the cache tries to provide the mobile unit with the most frequently accessed or updated data. . After the network is reconnected, the data modification information is exchanged with the database server or other terminals, and the consistency of the data is restored through conflict detection and coordination.

(2) Transaction model. In a mobile environment, fault tolerance and correction of transactions becomes tricky. A mobile thing is executed sequentially on several base stations. Due to the mobility of the mobile device, the execution process may involve multiple data sets. At this time, the lack of centralized coordination of transaction execution. Therefore, the traditional ACID nature of things must be modified, and new transaction management strategies and algorithms must be defined.

(3) Query processing. Knowing where the data is stored affects the cost-effectiveness analysis of query processing. Due to the mobility of mobile units and rapid resource changes, query optimization becomes more complex. When the query results are returned to the mobile units, these mobile units may be moving or crossing cell boundaries, but the query results received by the user must be correct and complete.

(4) Reply and fault tolerance. Mobile database environments must address issues caused by address errors, media failures, transaction and communication failures.

(5) Mobile database design. Due to mobility and frequent shutdowns, query execution is a global name resolution issue and becomes complicated. Mobile database design must take into account many management issues of metadata.

(6) Location-based services. As clients move, location-dependent cache information becomes invalid. Also, frequently updating location-dependent queries and then applying those queries to update the cache can cause problems.

^[1] (7) Security. Mobile data is less secure than fixed location data.

Research goals and significance of mobile database

An ideal mobile database system should effectively support various data applications in the mobile computing environment and meet the needs of people to access any data at any place and at any time. The following four goals should be achieved.

Scalability Mobile database availability and scalability

While ensuring the stability of the system, it provides high availability, and the number of mobile customers is unlimited, which can meet the simultaneous access of large-scale mobile users.

Mobility Mobile database mobility (Mobility)

Allows mobile computers to access and update databases while disconnected from the network.

(Serializability) Mobile database serializability

Supports concurrent transaction execution that satisfies stringability.

(Convergence) Mobile database convergence (Convergence)

Make the system always converge to a consistent state to avoid confusion.

Obviously, mobile databases will have many important applications in mobile computing environments, such as mobile office systems, future mobile command of digital battlefields, and the release of public information (weather forecast, tourist traffic information, stock market prices), etc. Practical value, has a wide range of application prospects.