8.1 Theoretical Background
In designing distributed computer systems, there are two critical aspects that need to be considered. These include the placement of data and programs across the sites or nodes
of computer network. In this module, it is assumed that DBMS software and application programs are stored at each site where data are kept. Therefore, the primary concern is
on the distribution of data.
To design a distributed database, it is important to know how to partition database into fragments, where to put the fragments and decide whether to replicate the fragments or
not. If replication is applied, one needs to choose which fragments are involved. The following exercise requires the students to design a simple distributed database system.
Example of fragments allocation to sites in a distributed database environment is provided in Figure 8-1 a,b.
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STAFF
Staff_Num Name
IC_num Salary
Branch_num
S002 Ali
750212-01-5636 30000
D008 S006
Zainab 740312-02-5326
25000 D008
S009 Atikah
770216-02-5632 25000
D008 S012
Ramadan 740316-04-5236
41000 D008
ZONBRANCH
Branch_Num Branch_Name Manager_Num D008
Selatan S002
DISTRICTBRANCH
Branch_Num District_Name
D008 Keluang
D008 Pontian
D008 Segamat
D008 Muar
Figure 8-1 a : Relation fragments at site 2 for department D008
STAFF
Staff_Num Name
IC_num Salary
Branch_num
S005 Hamid
730519-03-5636 33000
D003 S007
Vinosh 750818-04-5326
25000 D003
S011 Salim
781216-06-5632 23000
D003
ZONBRANCH
Branch_Num Branch_Name Manager_Num D003
Utara S005
DISTRICTBRANCH
Branch_Num District_Name
S005 Alor Star
S005 Ipoh
Figure 8-1 b : Relation fragments at site 3 for department D003
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8.2 Exercise
Below are the requirements and constraints of database system for a local Software Consultation and Maintenance company in Malaysia:
The company provides maintenance service across various states in
Malaysia. One branch is located within each state.
In total, the company hires 8,000 employees across the states.
The company needs to produce annual reports and ad hoc queries such as :
How many services below or exceeds expected profit RM10,000?
How many services in each branch?
How many employees for each job title involve in maintenance service?
In fact, each branch needs to handle all services provided in that particular branch state. Nevertheless, all branches should be able to get information about all employees and the
payment rate. Currently, all tables are located at company headquarters in PUTRAJAYA.
Below are the table structure and its associated data for the company’s database.
STAFF_ID NAME
HIRE_DATE S001
AHMAD MUZAFFAR 12-OCT-1987
S002 SITI MUZALIFFAH
11-MAR-1988 S003
ADURAH JAMIL 03-MAR-1989
S004 ANAS MALEK
10-02-1989
Figure 8-2: STAFF table
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STAFF_ID SERVICE_ID
JOB_TITLE S001
S1 MANAGER
S002 S1
ANALYST S002
S2 ANALYST
S003 S3
CONSULTANT S003
S4 ENGINEER
S004 S2
PROGRAMMER S004
S2 MANAGER
Figure 8-3: ASSIGNMENT table
SERVICE_ID SERVICE_NAME
EXPECTED_PROFIT STATE
S1 System analysis 9000
Selangor S2
Instrumentation 12000 Melaka
S3 CADCAM
11000 Kedah
S4 PC Maintenance
8000 Melaka
S5 System analysis 9000
Kedah S6
Instrumentation 12000 Kedah
Figure 8-4: SERVICE table
PAYMENT_RATE JOB_TITLE
SALARY MANAGER
40000 ANALYST
37000 CONSULTANT
35000 ENGINEER
32000 PROGRAMMER
15000
Figure 8-5: PAYMENT_RATE table
The company decide to decentralize the management in order to overcome all the problems they face with centralized management.
Based on the requirements answer the following questions: 1.
What do you recommend regarding to the type of the required database systems? 2.
What type of data fragmentation strategy is required for each table? 3.
Define the criteria to partition each table. 61
4. Is there any replication need? If yes, specify the replication strategy and tables or
fragments that involve in replication. 5.
Design the database fragments. Please specify node names, location, fragment names and demonstration data.
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8.3 Self Review Questions
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