Please Use These To Complete The Assignment For This Week

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Please use these to complete the assignment for this week Pg. 07 خطأ! استخدم علامة التبويب "الصÙØØ© الرئيسية" لتطبيق Heading 1 على النص الذي ترغب ÙÙŠ أن يظهر هنا. Deadline: Day 23/03/2019 @ 23:59 Database Management Systems IT 344 College of Computing and Informatics

Question One

Chapter 25 page .5 Marks

Learning Outcome(s): LO3 Explain the idea behind using SEMIJOIN in distributed query processing. The idea behind distributed query processing using the semijoin operation is to reduce the number of tuples in a relation before transferring it to another site. Intuitively, the idea is to send the joining column of one relation R to the site where the other relation S is located; this column is then joined with S.

Following that, the join attributes, along with the attributes required in the result, are projected out and shipped back to the original site and joined with R. Hence, only the joining column of R is transferred in one direction, and a subset of S with no extraneous tuples or attributes is transferred in the other direction. If only a small fraction of the tuples in S participate in the join, this can be quite an efficient solution to minimizing data transfer.

Question Two

Chapter 25 page .5Marks

Learning Outcome(s): LO3 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

Distributed Database systems provide distribution transparency of the data over the DBs. This is achieved by the concept called Data Fragmentation. That means, fragmenting the data over the network and over the DBs. Initially, all the DBs and data are designed as per the standards of any database system. In other words, dividing the whole table data into smaller chunks and storing them in different DBs in the DDBMS is called data fragmentation.

By fragmenting the relation in DB, it allows:

  • Easy usage of Data
  • Efficiency
  • Security
  • Parallelism
  • Reliability
  • Balanced Storage

Question Three

1.5Marks

Learning Outcome(s): LO3 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."

  1. 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. 
    GRANT SELECT ON STUDENT, INSTRUCTOR TO Bravo WITH GRANT OPTION;
  2. 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. 
    CREATE VIEW CourseView AS SELECT Title, Location, Time FROM Course WHERE Level=6;
    GRANT SELECT ON CourseView TO Charlie WITH GRANT OPTION;
  3. Alpha decides to revoke the SELECT privilege on the STUDENT relation from Bravo 
    REVOKE SELECT ON STUDENT FROM Bravo;

Question Four

1.5 Marks

Learning Outcome(s): LO3 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;

  1. Which database security mechanism would you recommend to the university?

    Mandatory Access Control

  2. Motivate your recommendation by describing two advantages.
    • Simple security property: It states that process labeled with higher classification cannot access or read information or resources.
    • Simple Integrity Property: In which low integrity subject cannot have the rights to write or modify high integrity data.
  3. What are the two disadvantages of using this approach?
    • MAC models put restrictions on user access that, according to security policies, does not allow for dynamic alteration.
    • MAC needs to place the operating system and associated utilities outside the access control framework.

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