22 - Data Integrity

Answers to exercises

What are the three goals of maintaining organizational memory integrity?

The three goals of organizational memory are:

A large corporation needs to operate its computer systems continuously to remain viable. It currently has data centers in Miami and San Francisco. Do you have any advice for the CIO?

Move from Miami and San Francisco because of the high probability of natural disasters (hurricanes and earthquakes). Establish duplicate data centers in less risky areas.

What mechanisms should a DBMS provide to support backup and recovery?

There are three types of mechanisms that support backup and recovery:

Backup facilities are used to create copies of the database. Journaling facilities provide backup copies or audit trails of transactions and/or database changes. Recovery facilities are used to restore the database to a consistent state and restart the processing of transactions.

A large organization has asked you to advise on backup and recovery procedures for its weekly, batch payroll system. They want reliable recovery at the lowest cost. What would you recommend?

Because this is a large organization and the database does not need to be up at all times, either forward or backward recovery would be appropriate to use to ensure that the payroll system could be recovered at a low cost. Reprocessing transactions may be too time consuming because the organization is so large and the time it would take to reprocess the transactions may be very time consuming. The firm should back-up each week to tape cartridge (low cost) and store an extra copy at a remote site.

The information systems manager of a small manufacturing company is considering the backup strategy for a new production planning database. The database is used every evening to create a plan for the next day's production. As long as the production plan is prepared before 6 a.m. the next day, there is no impact upon plant efficiency. The database is currently 200 Mbytes and growing about 2 percent per year. What backup strategy would you recommend and why?

Reprocessing transactions would be a good backup and recovery strategy for this small manufacturing company. It is easy to use and the database is fairly small and not growing at a very rapid pace so the time it would take to reprocess the database would not be very high. You would expect to find a daily backup to cartridge tape or optical disk of the database.

What are the advantages and disadvantages of reprocessing transactions?

Reprocessing transactions to recover data is considered a very simple form of recovering data. If a company uses reprocessing of transactions to recover data it is not necessary for them to recreate a database from stored image changes nor is there any special restart procedures. On the other hand, this method of data recovery can be very time consuming.

When would you use COMMIT in an application program?

COMMIT is used to commit the changes made to a database and to make these changes permanent. It is invoked when no errors occurred during an transaction.

What is the purpose of locking?

The purpose of locking is to prevent lost updates and inconsistent retrieval results.

What is a deadly embrace? How can it be avoided?

A deadly embrace occurs when there is an impasse because two users lock certain resources, then request resources locked by the other. Deadly embraces can be avoided through either prevention or resolution. Prevention requires users to lock in advance all records they will require for a given transaction, resolution uses the DBMS to detect and break deadlocks.

Assume that you want to discover the grade point average of a fellow student. You know the following details of this person. She is a Norwegian citizen who is majoring in IS and minoring in philosophy. Write one or more aggregate queries that should enable you to determine her GPA.
SELECT AVG(gradepoint) FROM student
   WHERE major = "MIS"
   AND minor = "Philosophy"
   AND citizenship = "Norwegian"
   AND gender = "F";
What are the disadvantages of the data encryption standard (DES)?

The disadvantages of Data Encryption Standard are that the code used to encrypt the message can be broken by using a high speed computer to try every variation of possible keys and it is difficult to find a secure way to distribute the secret key. This problem is exacerbated by the frequent need to change keys.

A national stock exchange requires listed companies to transmit quarterly reports to its computer center electronically. Recently, a hacker intercepted some of the transmissions and made several hundred thousands of dollars because of advance knowledge of one firm's unexpectedly high quarterly profits. How could the stock exchange reduce the likelihood of this event?

The national stock exchange could use two methods of securing the privacy of their data: restricting data access and encrypting the data. No users should be given access to select, update, delete, or insert any records associated with any company other than their own. All the transmissions between a firm and the stock exchange should be encrypted.

This page is part of the promotional and support material for Data Management (sixth edition) by Richard T. Watson
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Date revised: 19-Oct-2016