This document discusses database management systems and the three-level architecture. It describes the internal, conceptual, and external levels, and how mappings between these levels provide data independence which shields applications from changes in storage structures or access strategies. Logical data independence means changes to the conceptual model do not affect external views, while physical data independence means changes to the internal model do not affect the conceptual model. The document also reviews DBMS functions like transaction support and recovery services, and different DBMS environments like single-user, multi-user, and client-server systems.

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Database
Management
Systems
Lecture - 4

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Today’s Review
Continue 3-L architecture
Data Independence
Different aspect of DBMS

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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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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
External Level
Conceptual Level
Internal Level
Physical Data
Organization
Ext/Con Mapping
View 1 View 2 View n
Conceptual
Schema
Internal
Schema
Database
User 1 User 2 User n
Con/Int Mapping

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Name DoB Deps DepId
Rana Aslam 12/09/70 5 D001
Marya Wasti 29/02/80 0 D005
First Name: Rana
Last Name: Aslam
Date of Birth:
12 Sep, 1970
Name: R. Aslam
Age: 24y,10d
Dept: Sales
Saleem
Saleema
01110011010011100101001010100101010010101…..
BH RH Rana Aslam 120970 5 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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Changes in lower level do not affect the
upper levels
Don’t take it word to word
Mind the direction please
Data Independence

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Data Independence
Types
• Logical Data Independence
• Physical Data Independence

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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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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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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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Changes Examples
Changing file organization
Index implementation, hash, tree etc.
Changing storage medium

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3-Level Architecture
External Level
Conceptual Level
Internal Level
Physical Data
Organization
Ext/Con Mapping
View 1 View n
Conceptual
Schema
Internal
Schema
Database
User 1 User n
Con/Int Mapping
Conceptual Data Ind
Physical
Data Ind

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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
LAN
File returned Data request
Database
Workstation Workstation
File Server

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

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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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Database
Management
Systems
Lecture - 4