通信与信息工程学院专业英语结课作业班级：电子信息工程1303班姓名：学号：指导教师：苏扬作业时间：2015年12月23日成绩：评通信与信息工程学院二〇一五年翻译原文：Passage B DBMS and Data Independence, Integrity, ecurityYou know that a database is a collection of logically related data elements that may be structured in various ways to meet the multiple processing and retrieval needs of organizations and individuals. There’s nothing new about databases—early ones were chiseled in stone, penned on scrolls, and written on index cards. But now databases are commonly recorded on magnetize-able media, and computer programs are required to perform the necessary storage and retrieval operations.You’ll see in the following pages that complex data relationships and linkages may be found in all but the simplest databases. The system software package that handles the difficult tasks associated with creating, accessing, and maintaining database records is called a database management system (DBMS). The programs in a DBMS package establish an interface between the database itself and users of the database.(These users may be applications programmers, managers and others with information needs, and various OS program.)A DBMS can organize, process, and present selected data elements from the database. This capability enables decision makers to search, probe, and query database contents in order to extract answers to nonrecurring and unplanned questions that aren’t available in regular reports.These questions might initially be vague and/or poorly defined, but people can “browse”through the database until they have the needed information. In short, the DBMS will “manage”the stored data items and assemble the needed items from the common database in response to the queries of those who aren’t programmers. In a file-oriented system, users needing special information may communicate their needs to a programmer, who, when time permits, will write one or more programs to extract the data and prepare the information. The availability of a DBMS, however, offers users a much faster alternative communications path.Data IndependenceAn important point about database systems is that the database should exist independently of any of the specific applications. Traditional data processing applications are data dependent. COBOL programs contain file descriptions and record descriptions that carefully describe the format and characteristics of the data. Users should be able to change the structure of the database without affecting the applications that use it. For example, suppose that the requirements of your applications change. A simple example would be expanding ZIP codes from five digits to nine digits. In a traditional approach using COBOL programs, each individual COBOL application program that used that particular field would have to be changed, recompiled, and retested. The programs would be unable to recognize or access a file that had been changed and contained a new data description; this, in turn, might cause disruption in processing unless the change were carefully planned.Most database programs provide the ability to change the database structure by simply changing the ZIP code field and the data-entry form. In this case, dataindependence allows for minimal disruption of current and existing applications. Users can continue to work and can even ignore the nine-digit code if they choose. Eventually, the file will be converted to the new nine-digit ZIP code, but the ease with which the changeover takes place emphasizes the importance of data independence. Data IntegrityData integrity refers to the accuracy, correctness, or validity of the data in the database. In a database system, data integrity means safeguarding the data against invalid alteration or destruction. In large on-line database system, data integrity becomes a more severe problem and two additional complications arise. The first has to do with many users accessing the database concurrently. For example, if thousands of travel agents book the same seat on the same flight, the first agent’s booking will be lost. In such cases the technique of locking the record or field provides the means for preventing one user from accessing a record while another user is updating the same record.The second complication relates to hardware, software, or human error during the course of processing and involves database transactions to keep the database in a consistent state of integrity. A database transaction is a group of database modifications treated as a single unit. For example, an agent booking an airline reservation involves several database updates (i.e., adding the passenger’s name and address and updating the seats-available field), which comprise a single transaction. The database transaction is not considered to be completed until all updates have been completed; otherwise, none of the updates will be allowed to take place.Data SecurityData security refers to the protection of a database against unauthorized or illegal access or modification. This usually involves one or more levels of password protection that are specified in the data dictionary. For example, a high-level password might allow a user to read from, write to. and modify the database structure, whereas a low-level password might only allow a user to read from the database.Often an audit trail—the recorded history of the modifications to a database—can be used to identify where and when a database was tampered with and it can also be used to restore the file to its original condition.Words and Expressionsdatabase management system (DBMS) 数据库管理信息系统data independence 数据独立data integrity 数据完整性，数据一致性database transaction 数据库事务data security 数据安全性ZIP codes 美国邮区划分的五位编码译文：DBMS和数据独立性，完整性，安全性众所周知，数据库是逻辑上相关的数据元的集合。