Distributed Database Management Systems: Lecture 25

Distributed Database
Management Systems

Lecture 25


Distributed Database
Management Systems

Virtual University of Pakistan


In Previous Lectures: time 1:40230
• Reasons for Fragmentation
– Maximizes local access
– Reduces table size, etc.

• PHF using the SQL Server on
same machine


In Previous Lectures--2:00
• DDBS design is a team effort
• Involves
– Domain Experts
– DDBS Experts
– Network Experts


In Previous Lectures
• Implemented PHF in a Banking

Environment (around 3: 40)
• DDBS layer is superimposed on
the client sites (4:00)
• Actual Data resides with the local
sites (4:35)


Today’s Lecture

Derived Horizontal Fragmentation


Derived Horizontal Fragmentation
• Fragmenting/ Partitioning a table
based on the constraints defined
on another table.
• Both tables are linked with each
other through Owner-Member
relation


Time: 5:36
Owner
TABLE1

 

a, b, c, d

Link

TABLE2

p, q, r, s, a

Member


Scenario (around 7:25)
Owner
TITLE

titleId, titleName, sal

Link
EMP

 empId, empName, empAdres, titleId 

Member


Why DHF Here (8: 50)
• Employee and salary record is
split in two tables due to
Normalization
• Storing all data in EMP table
introduces Transitive Dependency
• That causes Anomalies

PHF of TITLE table, around 11:00

• Predicates defined on the sal
attribute of TITLE table
• p1 = sal > 10000 and sal <= 20000
• p2 = sal > 20000 and sal <= 50000
• p3 = sal > 50000


Conditions for the TITLE Table (11:58)

• TITLE1 =

(sal > 10000 and SAL ≤30000)

(SAL)

• TITLE2 =

(sal > 20000 and SAL ≤50000)

(SAL)

• TITLE3 =

(sal > 50000)

(SAL)

Tables created with constraints: 12:20
• create table TITLE1 (titleID char(3)
primary key, titleName char (15), sal
int check (SAL between 10000 and
20000))
• create table TITLE2 (titleID char(3)
primary key, titleName char (15), sal
int check (SAL between 20001 and
50000))
• create table TITLE3 (titleID char(3)
primary key, titleName char (15), sal
int check (SAL > 50000))


TITLE
titleID

titleName

Sal

T01

Elect. Eng

42000

T02

Sys Analyst

64000

T03

Mech. Eng

27000

T04

Programmer 19000

TITLE3

TITLE1
titleID

titleName

Sal

T04

Programmer 19000

titleID

titleName

Sal

T02

Sys Analyst

64000

TITLE2

titleID

titleName

Sal

T01

Elect. Eng

42000

T03

Mech. Eng

27000


EMP table at local sites (14:45)

• create table EMP1 (empId char(5) primary key,
empName char(25), empAdres char (30), titleId
char(3) foreign key references TITLE1(titleID))


Time 15:40
PHF on
TITLE

titleId, titleName, sal

Owner

Link
 empId, empName, empAdres, titleId 

EMP

Member
Natural Join with Owner Fragments


Referential Integrity Constraint
(18:30)
• Null value in the EMP1.titleId is
allowed
• This violates the correctness
requirement of the Fragmentation,
i.e., it will violating the
completeness critetion

Tighten Up the Constraint Around
20:00
• Further we need to impose the
“NOT NULL” constraint on the
EMP1.titleID
• Now the records in EMP1 will
strictly adhere to the DHF


Revised EMP1 Definition(21::00)
• create table EMP1 (empId char(5)
primary key, empName char(25),
empAdres char (30), titleId
char(3) foreign key references
TITLE1(titleID) not NULL)


Defining all three EMP
tables:21:20
• create table EMP1 (empId char(5) primary key,
empName char(25), empAdres char (30), titleId
char(3) foreign key references TITLE1(titleID)
not NULL)
• create table EMP2 (empId char(5) primary key,
empName char(25), empAdres char (30), titleId
char(3) foreign key references TITLE2(titleID)
not NULL)
• create table EMP3 (empId char(5) primary key,

empName char(25), empAdres char (30), titleId
char(3) foreign key references TITLE3(titleID)
not NULL)


Implementing same
scenario as PHF
22:10


PHF of EMP at different sites
(22:30)
• create table EMP1 (empId char(5)
primary key check (empId in
('Programmer')), empName
char(25), empAdres char (30),
titleId char(3))


• create table EMP2 (empId char(5) primary
key check (empId in (‘Elect. Engr’,’Mech.
Engr’)), empName char(25), empAdres
char (30), titleId char(3))

• create table EMP3 (empId char(5)
primary key check (empId in (' Sys
Analyst ')), empName char(25),
empAdres char (30), titleId char(3))

Adding a new record in TITLE
(23:10)
TITLE

TITLE

titleID

titleName

Sal

titleID

titleName

Sal

T01

Elect. Eng

42000

T01

Elect. Eng

42000

T02

Sys Analyst

64000

T02

Sys Analyst

64000

T03

Mech. Eng

27000

T03

Mech. Eng

27000

T04

Programmer 19000

T04

Programmer 19000

T05

Assist Supr

New Record

16000


Time 24:00
• All three predicates of PHF
defined in the two slide a couple
of slides ago