Reference no: EM132263359

Questions: 1. Explain the idea behind using SEMIJOIN in distributed query processing.

2. In your own words explain what is meant by Data Fragmentation? Given the following customer relation, apply the horizontal fragmentation based on customer's gender.

Customer_id	Name	Area	Payment type	Sex
112	Ahmed	jeddah	Credit card	male
211	Khaled	riyadh	cash	male
311	Noura	madinah	cash	female

3. Suppose DBA has created three accounts Alpha, Bravo, and Charlie. Alpha is the owner of the following database schema;

STUDENT: Sid, Lname, Fname, Phone, Gpa

COURSE: Cid, Title, Level, Units, Location, Time

INSTRUCTOR: Iid, Lname, Fname, Designation, Salary, Dept.

Write SQL statements to grant or revoke following privileges. "

Create the views if and when necessary.

a) Alpha wants to allow Bravo to retrieve information from STUDENT and INSTRUCTOR tables and also to be able to propagate the SELECT privilege to other accounts.

b) Alpha wants to give a capability to retrieve Title, Location, and Time from the COURSE relation where the Level = 6 to Charlie and to be able to propagate the privilege.

c) Alpha decides to revoke the SELECT privilege on the STUDENT relation from Bravo

4. Suppose a public sector university in Saudi Arabia wants to implement the strictest access control to its databases. Instead of allowing each user to control access to their own data, the university wants system resources to be controlled by the operating system under system administrator with an hierarchical approach of assigning security labels to the resource objects.

Answer the following questions;

a) Which database security mechanism would you recommend to the university?

b) Motivate your recommendation by describing two advantages.

c) What are the two disadvantages of using this approach?