1. © Virtual University of Pakistan

2. Database Management Systems
Lecture - 4
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3. © Virtual University of Pakistan
Today’s Review
Continue 3-L architecture
Data Independence
Different aspect of DBMS
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4. Level 3 Internal or Physical View
Concerns about the physical implementation of the database
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Internal View
DBMS chooses type of data structures
lays out data on storage devices with operating system access methods
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Internal View
Internal record: a single stored record
Does not just contain what we see at the conceptual level
DBMS adds other data
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Physical Level
Generally same as Internal
Actual representation of data on the storage device
In the binary format
OS responsibility
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8. Inter-Schema Mappings
Also a part of 3-level architecture
External/conceptual mapping
Conceptual/Internal
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Ext/Con Mapping
Specifies mapping between objects in the external view to those in the logical model
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Con/Int Mapping
Specifies mapping between objects in the logical model to those in the physical model-data independence
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3-Level Architecture
View 1
View 2
View n
Conceptual Schema
Internal
Schema
Database
User 1
User 2
User n
External Level
Ext/Con Mapping
Conceptual Level
Con/Int Mapping
Internal Level
Physical Data Organization
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12. © Virtual University of Pakistan
First Name: Rana
Last Name: Aslam
Date of Birth:
12 Sep, 1970
Name: R. Aslam
Age: 24y,10d
Dept: Sales
Saleem
Saleema
Name
DoB
Deps
DepId
Rana Aslam
12/09/70 5
D001
Marya Wasti
29/02/80
D005
BH RH Rana Aslam D001 RH Marya Wasti…
…..
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Data Independence
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Data Independence
A major outcome of 3-L Arch
The immunity of applications to change in storage structure and access strategy
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Data Independence
Changes in lower level do not affect the upper levels
Don’t take it word to word
Mind the direction please
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16. Data Independence Types
Logical Data Independence
Physical Data Independence
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17. Logical Data Independence
Changes in conceptual model do not affect the external views
Immunity of external level from changes at conceptual level
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18. © Virtual University of Pakistan
Types of Changes
Adding a new file/index etc.
Adding a new field in a file
Changing type/size
Deleting an attribute
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19. Physical Data Independence
Changes in the internal model do not affect the conceptual model
Immunity of Conceptual level from changes at Internal level
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20. © Virtual University of Pakistan
Changes Examples
Changing file organization
Index implementation, hash, tree etc.
Changing storage medium
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3-Level Architecture
User 1
User n
View n
External Level
View 1
Conceptual Data Ind
Ext/Con Mapping
Conceptual Schema
Physical
Data Ind
Conceptual Level
Con/Int Mapping
Internal
Schema
Internal Level
Physical Data Organization
Database
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Functions of DBMS
Data Processing
A User Accessible Catalog
Transaction Support
Concurrency Control Services
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Functions of DBMS
Recovery Services
Authorization Services
Support for Data Communication
Integrity Services
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DBMS Environments
Single User
Multi-user
Teleprocessing
File Servers
Client-Server
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Teleprocessing
All processing at
a central computer
Dumb Terminals
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File Servers
Database
File Server
File returned
Data request
LAN
Workstation
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Workstation

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Client-Server
Database
Server
(with DBMS)
Data request
Selected data returned
LAN
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Client
Client

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Today’s Summary
Completed 3-L architecture
Discussed data independence
Discussion on DBMS
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Thanks and Allah Hafiz
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30. Database Management Systems
Lecture - 4
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