嵌入式移动数据库及其应用.doc

科技译文学员单位： 二十五队 学员姓名： 周 林 蔚 专业名称： 通信工程 完成时间： 2011.05.11 Embedded Mobile Database and ApplicationOne、The theory of embedded mobile database1、Embedded Systems With digital information technology and network technology, after the rapid development of PC era, embedded systems have been widely infiltrated into every aspect of daily life,from home washing machines, refrigerators, to the bicycle as a transport, Cars,to the office so the remote conferencing system, embedded system applications vary widely day. Especially wireless LAN technology and the emergence of standard protocols, so that the concept of embedded wireless communications quietly rising. When the embedded wireless communication control chip prices may be accepted,its application will be more ubiquitous. Home, office, public places, people can use dozens of films and even more so embedded wireless communication controller chip,some of the electrical equipment of electronic information equipment and even constitute a wireless network; in the car, on the road,people can also use this Embedded communication controller chip for remote office, remote control, to achieve a real sense of the network to carry. Embedded systems is a collection of computer hardware and software, may also contain a number of other mechanical parts, he is to accomplish a specific function and design. The concept of embedded systems is about to be made in around 1970, and earlier just to achieve an embedded system control functions, using a simple control on the outside of the control loop to process the request, generally do not use operating system. As technology advances, more and more complex applications, the use of the range more widely, in some high-end applications, embedded systems generally embedded operating system, from the 80s of last century, there has been a variety of different Contending commercial embedded operating system like the situation, more notably VxWorks, pSOS, Plam OS and Windows CE, etc., most of these operating systems developed for the proprietary systems, which greatly promoted the embedded systems The use and development in all walks of life.2、 Embedded Mobile Database Since the 90s of the 20th century, with the embedded systems and wireless communication network technology, rapid development, there has been mobile office, mobile communications, mobile services, new ideas, people get information and use of information on the occasion, time, manner and method of proposed More and more new requirements, which means that high-end mobile phones, PDAs, PDA and other mobile devices feature higher and higher requirements. As mobile devices and data throughput enhancements, expansion of data storage in mobile devices by implementing an embedded database to manage data to improve efficiency and become embedded mobile devices, an important direction of development, we put Species in the mobile computing environment, used in handheld computers, PDA and other mobile devices embedded mobile database system called Database. embedded mobile database widely used in mobile environments, in addition to the application mentioned above, driven by demand outside the, Embedded system widely used in various fields and the rapid development of mobile devices in the embedded database system environment to achieve the necessary hardware platform.3、The mobile computing environment the characteristics of embedded mobile database Embedded mobile database is to support mobile computing, mobile devices running on the database system, which involves database technology, distributed computing and mobile communications technology and other disciplines. More simply, mobile database contains the following two implications: First, the user can move the process online access to the database server resources. Second, the user can move with the clients database.With the traditional distributed database systems, embedded mobile database system has the following characteristics: mobility and location relevance, frequent disconnection, network conditions, the diversity of network communication asymmetry, low-power operating environment, system security and reliability is poor, resources are limited.（1）Mobility: In mobile computing environment, a mobile device not only in different places connected network, and also in the mobile network connection can be maintained. The mobility of mobile terminals may lead to changes in the layout of system access and resource movement. Moreover, the individuals mobility (ie, different parts of the use of local computing devices) along with the Personal Communication Network and Network Computer applications increasingly prominent.（2）Frequent disconnection of: mobile computing devices on the move, due to the use, power, wireless communication cost, network conditions, and other factors, is generally not used to maintain a continuous network of the work, but the gap between active and passive network , disconnect. In this case, we must consider the client database and server database and data consistency of data storage, data prefetching, data recovery and other issues. （3）Diversity of network conditions: the mobility of mobile computing devices are available at different times makes the network conditions (such as network bandwidth, communication cost, network latency and service quality, etc.) is changing, and even significant differences between: a mobile device connected to both high-bandwidth The fixed network (such as LAN), can also work in low-bandwidth wireless WAN (such as CDPD), or simply not available on the network (in disconnected state). Therefore, the mobile terminal embedded database to be considered in a variety of network environments, database work characteristics and work performance issues. （4）Asymmetric network communication: communication media, due to the physical limitations of wireless network communications are typically asymmetrical, and in the fixed server node can send a powerful device, and mobile computing devices to send a very limited or no ability to send the capacity . Thus the downlink (from server to mobile clients) and cost of communication bandwidth and uplink with the (mobile client to the server) a big difference. Based on this characteristic, the mobile client to receive data from the server to wait for the server is usually a negative data broadcasting mainly to reduce the client sends a request to the server data updates and so on. In other words, the whole system of communication is the main use of the downlink, reducing or even not use uplink. （5）Between low-power operating environment: mobile computing devices rely mainly on battery power, and generally very limited battery capacity, for example, a typical notebook computer in the normal case of continuous use can only be maintained generally 2-5 hours. It is estimated that the battery capacity in the next 5 years has only increased by about 30%, far lower than the CPU speed and storage capacity over the same period the pace of development. Thus, although quite a number of energy-saving technologies for mobile computing devices, and on suitable Low-power operating environment of mobile computing devices is still an important issue. Operating environment for low-power embedded mobile database should also consider the algorithms and strategies adopted to achieve the client to save energy. Usually, the client will not receive the data and does not handle transactions with the client to sleep when the way to achieve energy conservation. （6）System security and reliability of difference: in the mobile computing environment, embedded mobile database also has a poor safety and reliability risks. Since many applications of embedded devices is handled through the system the key data management device, so the embedded database on the device access control system to a more strict. Meanwhile, many embedded devices with high mobility, portability for fixed working with Mu environment, but also potentially unsafe. At the same time some of the data privacy and high, so to prevent the collision, magnetic interference, loss, theft and other threats to the security of personal data still need to provide adequate security guarantees. Above all, in improving the overall system performance and safety, reliability, need serious consideration. （7）Limited resources: the mobile computing environment mobile client traditional distributed database system for the client, has limited resources and features. Whether the processing power of the processor or processors, processing speed, are relatively low, but also a small storage space with a main memory, the external drive capability and poor features. So how better use of limited resources the client needs of embedded mobile database is a key issue.Two、The key technologies embedded mobile database Resource constraints of mobile devices, which integrate the general and application systems, front-end application system as a whole exists, and it manages the data set may be the back-end server in the data set or subset of a subset of the copy. Embedded mobile database systems must be improved to solve the key problem in the following technology: Backup and Recovery: Embedded Database DBMS backup and recovery management with large databases, not simply an independent service or a similar form, but to be completed in accordance with a simplified way. Replication and synchronization: a data commonly used embedded database replication mode (uploading, downloading or in combination) with the server map database to meet the people in any place, any time access to any data needs. Because of data replication, the various applications in the system between the front-end and back-end server may need to synchronize all the necessary control process, and even some or all of the application front end, in the middle but also for data synchronization. Copy number of mobile nodes in the maintenance of data backup, including the replication between servers and mobile computers to save a copy of the database. The former general known as the copy which is known as cache. The main purpose is to improve the copy distributed database system availability, reliability, and access performance. The primary issue is how to copy the node to maintain multiple data state consistency. Replication by maintaining a consistent way to divide the existing replication agreements can be divided into strict and weak agreement on a consensus agreement of two. Strict consensus agreement requires that any time a copy of all databases are the same; and weak consensus agreement allows each copy of the inconsistencies between the temporary, but this inconsistency can always remain within certain limits, but always in line (convergence). At present, mobile computing features for carrying out data replication/caching of the most representative is: J. Gray of the two replication mechanisms,CODA system, and cache invalidation reports broadcasting technology,the other,SYBASE companys mobile database product SQLANYWHERE and SQLREMOTE also used the technology to support mobile computing environment. Mobile Transaction Processing: Transaction database management system is a basic function,mainly used to maintain data consistency,multi-user concurrent access, allowing users to reliably query and update the database. In general, users access the database system is done through the transaction. In a traditional database system, a transaction composed of a series of read and write operations. Transaction must meet four criteria, namely atomicity, consistency, isolation, and permanent (referred to as ACID).The characteristics of mobile computing environment, the traditional database transaction processing systems can not meet the requirements of mobile transactions.Three、Application of embedded mobile database technologyEmbedded mobile database technology now has moved from research to a wider range of applications development and close integration of various intelligent devices embedded mobile database technology has been the academic, industrial, military and civilian departments and other aspects of attention.Embedded mobile database technology now has moved from research to a wider range of applications development, with the mobile communications technology and people management needs of mobile data processing and continuous improvement of working closely with a variety of smart devices with embedded mobile database technology Has been the academic, industrial, military and civilian departments and other aspects of attention. People will find that in the near future embedded mobile database will be everywhere. It is hoped that the information anytime, anywhere access to the aspirations of any data will eventually become a reality.Changes in the computing environment, embedded mobile database most striking feature is: everywhere.1、Application StatusDevelopment of computer technology and its applications from the historical point of view, computer technology, especially the driving force behind the development of database technology, mainly from two aspects, namely: the application continues to grow demand and other supporting technology. Research in the field of embedded mobile database continues to further development, has entered the practical and the product of the stage.Looking at the current international and domestic application of embedded database, embedded database or mobile database applications in a Hundred Flowers of the state. In other words, the current market-based demand for embedded database applications, has entered the stage of accelerated development. However, a variety of applications, computing platforms also have their own characteristics, there is no one company can do to dominate the world, the entire market demand is still much room.Two applications:Applications based on embedded mobile database applications can be divided into horizontal and vertical applications.The so-called horizontal application, refers to the application program can be used in a variety of different industries, requires minimal customization; and vertical applications are industry-specific applications, data processing, unique.（1） Application LevelSuch applications can be used for different areas, without modifying the core application, only the front or rear of the application of appropriate customization. Database Information AccessMobile users through front-end embedded database application tools, submitted directly to the network database server, query, cache the results will be retrieved or copied to the embedded database, the local administration. The front-end tools may be some customization, back-end database server may also make some changes. Between the venue or venues for mobile applicationsApplications for mobile users in one or a few venues move, while maintaining contact with the base server, a typical application of this inventory and manufacturing management of the companys workshop. Based on the application of GPS and GLSGeosynchronous communications satellite by such applications (GPS class) to send the map information or location information, or to broadcast the signal through the transmitter (GLS class) to send the location information, a variety of location information, environmental information and other supporting information can be retained in Embedded database. For example, Geographic Information System map of the designated place by getting the information to guide the work, the system can be applied to natural resources and environmental control. On-site audit and inspectionMobile users is a certain audit, inspection, supervision and other rights of inspectors, in the process to connect to the database of information by inspectors and the necessary updates, and update the embedded database that is checked. For example: taxi checks, financial audits, construction supervision, coordination of vehicle insurance.Applications listed above have greater versatility, each of which can extend to different industries.（2）Vertical ApplicationsCompared with the level of applications, vertical industry applications has obvious specificity in different areas vary greatly between applications, the results indicated that the management of the database and server are quite different. Mainly related to insurance, banking, flight information, government departments and other specific industry sectors. Application of the financial sectorMainly related to the insurance industry, banking, stock trading. If the insurance industry in a number of customer accounts clerk in the summary of the information, and if necessary given some form of report. Based Pocket PC or other mobile devices built on embedded database for mobile applications to satisfy the application requirements. Application of the retail and distribution industry Manual or fixed POS sales, has been developed for wireless networks based on embedded database management of mobile electronics and wireless POS system CDs. In addition, the mobile wireless Modem can support credit card payment vending machines to be registered in real-time wireless communication, authentication, complete the transaction. Health care applicationsSuch applications include tele-consultation, emergency medical services, on-site medical data collection. Doctors through a wireless network that can extract patient medical records in any place, study disease, to develop prescription. Law and Public SafetyMobility of mobile users in the hunt for the perpetrators has obvious advantages. Police officers embedded database for mobile devices to retain certain information about the perpetrators, you can always retrieve the suspect information. TransportationUsing mobile computing technology can reduce the deliv