计算机英语（第二版）课件chapter8.pdf

Computer Science in English Teaching Assisted Courseware Designed and Programmed By Jiang Tongqiang Miao Tianshun Computer Science in English I. Pre-reading QuestionsI. Pre-reading Questions Chapter 8 II. Grammatical Notes to the TextII. Grammatical Notes to the Text An Introduction to Database Systems III. Words Bank to the TextIII. Words Bank to the Text IV. Exercises of the ChapterIV. Exercises of the Chapter Chapter 8 I. Pre-reading Questions 1. What are the major disadvantages 1. What are the major disadvantages in in a file-processing system? a file-processing system? (1) Data redundancy and inconsistency. 2. What are the two levels of data (2) Difficulty in accessing data. independence? Describe each of them. (3) Data isolation. (4) Integrity problems. 3. What are the functions of the (5) Atomicity problems. structured query language (SQL)? (6) Concurrent-access anomalies. (7) Security problems. Chapter 8 I. Pre-reading Questions 2. What are the two levels of data independence? Describe each of them. Reference Key: There are two levels of data independence: Physical data independence is the ability to modify the physical schema without causing application programs to be rewritten. Modifications at the physical level are occasionally necessary to improve performance. Logical data independence is the ability to modify the logical schema without causing application programs to be rewritten. Modifications at the logical level are necessary whenever the logical structure of the database is altered (for example, when money-market accounts are added to a banking system). Chapter 8 I. Pre-reading Questions 3. What are the functions of the structur