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INSTRUCTOR’S MANUAL
FOR DatabaseSystem Concepts Sixth Edition Abraham Silberschatz Henry F. Korth
- Sudarshan
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C H A P T E R
1 Introduction Chapter 1 provides a general overview of the nature and purpose of database systems. The most important concept in this chapter is that database systems allow data to be treated at a high level of abstraction. Thus,database systems differ significantly from the file systems and general purpose programming envi- ronments with which students are already familiar. Anotherimportant aspect of the chapter is to provide motivation for the use of database systems as opposed to application programs built on top of file systems. Thus, the chapter motivates what the student will be studying in the rest of the course.The idea of abstraction in database systems deserves emphasis throughout, not just in discussion of Section 1.3. The overview of the structure of databases is, of necessity, rather brief, and is meant only to give the student a rough idea of some of the concepts. The student may not initially be able tofully appreciate the concepts described here, but should be able to do so by the endof the course.The specifics of theE-R, relational, and object-oriented models are covered in later chapters. These models can be used in Chapter 1 to reinforce the concept of abstraction, with syntactic details deferred to later in the course.If students have already had a course in operating systems, it is worthwhile to point out how theOSandDBMSare related. It is useful also to differentiate between concurrency as it is taught in operating systems courses (with an orien- tation towards files, processes, and physical resources) and database concurrency control (with an orientation towards granularity finer thanthe file level, recov- erable transactions, and resources accessed associatively rather than physically).If students are familiar with a particular operating system, thatOS’s approach to concurrent file access may be used for illustration.Exercises 1.7List four applications you have used that most likely employed a database system to store persistent data.
Answer:
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- Chapter 1Introduction
•Banking: For account information, transfer of funds, banking transac-
tions.
•Universities: For student information, online assignmentsubmissions,
course registrations, and grades.
•Airlines: For reservation of tickets, and schedule information.
•Online news sites: For updating new, maintainence of archives.
•Online-trade: For product data, availability and pricing informations,
order-tracking facilities, and generating recommendation lists.
1.8List four significant differences between a file-processingsystem and a DBMS.
Answer:Some main differences between a database management system
and a file-processing system are:
•Both systems contain a collection of data and a set of programs which access that data. A database management system coordinatesboth the physical and the logical access to the data, whereas a file-processing system coordinates only the physical access.•A database management system reduces the amount of data duplica- tion by ensuring that a physical piece of data is available toall programs authorized to have access to it, whereas data written by one program in a file-processing system may not be readable by another program.•A database management system is designed to allow flexible access to data (i.e., queries), whereas a file-processing system isdesigned to allow pre-determined access to data (i.e., compiled programs).•A database management system is designed to coordinate multiple users accessing the same data at the same time. A file-processing sys- tem is usually designed to allow one or more programs to access dif- ferent data files at the same time. In a file-processing system, a file can be accessed by two programs concurrently only if both programs have read-only access to the file.
1.9Explain the concept of physical data independence, and its importance in database systems.
Answer:Physical data independence is the ability to modify the physical
scheme without making it necessary to rewrite application programs. Such modifications include changing from unblocked to blocked record storage, or from sequential to random access files. Such a modificationmight be adding a field to a record; an application program’s view hides this change from the program.
1.10List five responsibilities of a database-management system. For each re- sponsibility, explain the problems that would arise if the responsibility were not discharged.
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