important question on database management system(DBMS)

1) List four significant differences between a file-processing system 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 coordinates both 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 duplication by
  ensuring that a physical piece of data is available to all 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 is designed to allow predetermined 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 system is usually designed to allow one or more programs to access different 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.

2) This chapter has described several major advantages of a database system. What are two disadvantages?
Answer: Two disadvantages associated with database systems are listed below.

• Setup of the database system requires more knowledge, money, skills, and time.

•  The complexity of the database may result in poor performance.

3) Explain the difference between physical and logical data independence.
Answer:

•  Physical data independence is the ability to modify the physical scheme without making it necessary to rewrite application programs. Such modifi- cations include changing from unblocked to blocked record storage, or from sequential to random access files.

• Logical data independence is the ability to modify the conceptual scheme without making it necessary to rewrite application programs. Such a modification might be adding a field to a record; an application program’s view hides this change from the program.

4) List five responsibilities of a database management system. For each responsibility, explain the problems that would arise if the responsibility were not discharged.
Answer: A general purpose database manager ( DBM ) has five responsibilities:

• interaction with the file manager.
•  integrity enforcement.
•  security enforcement.
•  backup and recovery
• concurrency control

 If these responsibilities were not met by a given DBM (and the text points
out that sometimes a responsibility is omitted by design, such as concurrency
control on a single-user DBM for a micro computer) the following problems can
occur, respectively:

• No DBM can do without this, if there is no file manager interaction then
  nothing stored in the files can be retrieved.
• Consistency constraints may not be satisfied, account balances could go be-
  low the minimum allowed, employees could earn too much overtime (e.g.,
  hours > 80) or, airline pilots may fly more hours than allowed by law.
• Unauthorized users may access the database, or users authorized to access
  part of the database may be able to access parts of the database for which
  they lack authority. For example, a high school student could get access
  to national defense secret codes, or employees could find out what their
  supervisors earn.
• Data could be lost permanently, rather than at least being available in a consistent state that existed prior to a failure.
• Consistency constraints may be violated despite proper integrity enforcement in each transaction. For example, incorrect bank balances might be reflected due to simultaneous withdrawals and deposits, and so on.