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Distributed Database Management Systems . Lecture 25. Distributed Database Management Systems . Virtual University of Pakistan. In Previous Lectures: time 1:40-230. Reasons for Fragmentation Maximizes local access Reduces table size, etc. PHF using the SQL Server on same machine.

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Distributed database management systems1

Distributed Database Management Systems

Virtual University of Pakistan


In previous lectures time 1 40 230
In Previous Lectures: time 1:40-230

  • Reasons for Fragmentation

    • Maximizes local access

    • Reduces table size, etc.

  • PHF using the SQL Server on same machine


In previous lectures 2 00
In Previous Lectures--2:00

  • DDBS design is a team effort

  • Involves

    • Domain Experts

    • DDBS Experts

    • Network Experts


In previous lectures
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
Today’s Lecture

Derived Horizontal Fragmentation


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


Owner

a, b, c, d

TABLE1

Link

TABLE2

p, q, r, s, a

Member

Time: 5:36


Scenario around 7 25
Scenario (around 7:25)

Owner

titleId, titleName, sal

TITLE

Link

EMP

empId, empName, empAdres, titleId

Member


Why dhf here 8 50
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
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
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
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

TITLE3

TITLE1

TITLE2


Emp table at local sites 14 45
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
Time 15:40

PHF on

Owner

titleId, titleName, sal

TITLE

Link

empId, empName, empAdres, titleId

EMP

Member

Natural Join with Owner Fragments


Referential integrity constraint 18 30
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
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
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
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)



Phf of emp at different sites 22 30
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

New Record


Time 24 00
Time 24:00

  • All three predicates of PHF defined in the two slide a couple of slides ago


May be 24 40
May be: 24:40

  • create table EMP1 (empId char(5) primary key check (empId in ('Programmer‘, ‘Assist Supr’)), empName char(25), empAdres char (30), titleId char(3))




EMP1

EMP3

EMP2





  • Lets do it occur or at timed intervals

  • From the Enterprise Manager, select Replication, after a couple of nexts, we get this screen






A couple of more nexts and then subscribe, we have created a new one





Merge replication
Merge Replication is expressed in




  • Now you execute the snapshot agent of this replication once again our old familiar screen

  • It will create the snapshot, then you subscribe a database

  • We find the original data in the subscriber

  • After this if we make any change on either side, it will be reflected on the other side



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