Why the Advent of Databases-2

File-processing systems have other disadvantages over Databases as well. Hence the advent of Databases. I give two other of these disadvantages below:

·        Concurrent-access anomalies: Multiple users may update a system simultaneously. This facilitates faster response and overall performance of the system. However, interaction of concurrent updates may result in inconsistent data. Consider bank account A, containing Tk500. If two customers withdraw funds say Tk50 and Tk100, respectively from Account A at about the same time, the result of concurrent transactions may leave the account in an inconsistent state. If the two transactions occur concurrently, they may both read the value Tk500, and write back Tk450 and Tk400, respectively. Depending on which one writes the value last, the account may contain either Tk450 or Tk400, rather than the correct value of Tk350. To prevent this from happening, the system must maintain some form of supervision. But supervision is difficult to provide because data may be accessed by various different application programs that have not been coordinated previously.

·        Security problems: Every user of the database system should not be able to access all the data. For example, in a banking system, payroll personnel (tax officer) needs to see only that part of the database that has information about the various bank employees. They do not need to access information about customer accounts. As another example, bank tellers see only that part of the database that has information on customer accounts. They cannot access information about salaries of bank employees. Enforcing such security constraints on a file-processing system is difficult because application programs are added to the system in an ad hoc manner.

P.S  I am writing a book on Databases. In the current blog, I will give you every Friday morning BDT time, small excerpts on Databases from my book in order to brush up on the subject. My eBook on Databases is a copyright in 2015 by me, Rosina S Khan. No part(s) or whole of these excerpts may be used or reproduced in any form whatsoever, without written permission by the author.