电子系专业英语Unit-11-Database.ppt

3.Important words: Field 字段 approach access Notes (p139） 1. by contrast ： 相反 2. since…. 原因状语从句 3. rest with: 取决于 4. neither…nor…. 5. have no access privileges to… 对……没有访问权利 3.Important wordsfield in text Most database programs provide the ability to change the database structure by simply changing the ZIP code field and the data-entry form. 大多数的数据库程序允许只是简单的修改zip代码字段和数据输入形式就改变了数据库中数据的结构。 Access in text In these cases, the potential value of the information goes unrealized because it is not known to people in other departments who may need it or it cannot be accessed efficiently. 在这种情况下，信息的潜在价值没有实现，因为需要这些信息的其他部门的人不知道或者不能有效地访问这些信息。 　　(5) file organization stores the records in an indexed file in an ascending or descending sequence based on the value in the key field of the record. 　　a. Indexed b. Sequential c. Direct d. Relative 　　(6) ?When fast access to a particular record is required, we should not use file organization. a. indexed b. direct c. sequential d. relative 　　(7) ?Compared with the traditional data management, a database system can offer us . 　　a. reduced data redundancy b. improved data integrity 　　c. reduced development time d. all of above 　　(8) ?Data redundancy and data dependency can be avoided by using . 　　a. sequential files b. random files 　　c. files d. a database 　　(9) ?With access, records can be accessed in any order. 　　a. direct b. record 　　c. file d. sequential 　　(10) ?Data occurs when the same data are stored in two or more files. 　　a. redundancy b. dependency 　　c. access d. loss 　　2. ?Answer the questions. 　　(1) ?Describe sequential file organization. 　　(2) What is an indexed file? Describe how the index is used to retrieve records from an indexed file. 　　(3) ?Write a definition for a direct file. 　　(4) ?Write a definition for the term database. 　　(5) ?What are the adva