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DBMS
Lecture 3
History of DatabaseFile System
3 Levels of Abstraction
Types of DatabasesComponents of DBMS
Zeshan Ahmer
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Brief History of Database Systems
1940's, 50's Initial use of computers as
calculators. Limited data, focus on algorithms.
Science, military applications
1960's Business uses. Organizational data,
customer data, sales, inventory, accounting, etc.
File system based, high emphasis on
applications programs to extract and assimilatedata. Larger amounts of data, relatively simple
calculations
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1970's The relational model. Data separated
into individual tables. Related by keys. Initially
required heavy system resources. Examples:
Oracle, Sybase, Informix, IBM DB2
1980's Microcomputers - the IBM PC, Apple
Macintosh. Database program such as DBase,Paradox, FoxPro, MS Access. Individual user
can create, maintain small databases
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Late- 1980's Local area networks. Workgroups
sharing resources such as files, printers, e-mail
Client/Server Database resides on a centralserver, applications programs run on client PCs
attached to the server over a LAN
1990's Internet and World Wide Web makedatabases of all kinds available from a single
type of client - the Web Browser
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A Simple Architecture
A Simple Architecture
SQL
C/C++
Programs
DBMS
ApplicationsDatabases
Shared facilities:
Backup and recovery
Data storage and
access modules
Programming tools,
etc.
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Limitations of a File System
Separated and Isolated Data - Coordination and
representation of data is difficult
Data Duplication - Wastes space and can lead todata integrity (inconsistency) problems
Application Program Dependencies - Changes
to a single file can require changes to numerous
application programs
Lack of Data Sharing - Difficult to control access
to files
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Purpose of Database SystemsPurpose of Database Systems
Database management systems were
developed to handle the difficulties causedby different people writing different
applications independently
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A DBMS attempts to resolve the following
problems:
Data redundancy and inconsistency by keeping one
copy of a data item in the database
Difficulty in accessing data by providing query
languages
Integrity problems by enforcing constraints (age >
0)
Concurrent access by multiple users
Security problems
Purposes of Database SystemsPurposes of Database Systems
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Integrated Database Environment
Byte
Data-item or field
Record
File or Table
DatabaseDatabase management systems
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Unit of measurement of data
One Byte -8
bits
Maximum value in one bit
Maximum value in one byte
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Integrated Database Environment DataStorage Hierarchy
Database
Record
File
Field
Character(byte)
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Advantages of Database Approach
Minimal data redundancy
Data consistency and Integrity - by
controlling access and minimizing data
duplication
Enforcement of standards
Uniform security
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Application program independence - by storingdata in a uniform fashion
Data Sharing - by controlling access to data
items, many users can access data concurrently
Backup and Recovery
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Cost issue
Related with developing DBMS
Related with hardware cost
Related with higher programming
cost / users trainingRelated with conversion cost
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3-level architecture
User/View Level
Logical Level
Physical Level
v1 v2 v3
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3-Level Architecture
Logical Level:
e.g. tables
STUDENT (roll number, name)COURSE (roll number, course id, grade)
Physical Level:
how are these tables stored, how many bytes,
restrictions etc
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User/View Level, e.g.:
v1: select roll number from student
v2: select roll number , course id from course
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view 1 view 2.....
view n
Logical
view
Physical
view
Payroll Inventory Sales
Company database
Files on disks
Three Levels of AbstractionThree Levels of Abstraction
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View Level:
Define a subset of the database for a
particular application
Logical Level:
Describes data stored in database, and therelationships among the data
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Physical Level:
Describe how a record is stored on disks.
e.g., Divide the customer records into 3
partitions and store them on disks 1, 2 and
3
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DatabasesT
ypes & Physical Locations
Shared Databases
Shared by users in an organization within one
location
Typically found on local-area networks
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Databases
Types & Physical Locations
Distributed Databases
Database stored on different computers in
different locations connected by a client / server
type of network
Two methods are:Partitioning
Duplicating
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DatabasesT
ypes & Physical Locations
Centralized Databases
Database stored in one location that can be
accessed by different computers in different
locations via communication networks
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Database Administrator (DBA)
The person who co-ordinates all related
activities and needs for an organizations
database
Responsibilities include:
database design, implementation and operation
user coordination
system security
backup and recovery
performance monitoring
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schema definition (logical level)
Physical schema (storage structure,
access methods)
schemas modifications
granting authorizations
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Components of DBMS
Data
Hardware
Software
Users
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User Data
Data users work with directly by entering,
updating and viewing
For our purposes, data will be generallystored in tables with some relationships
between tables
Each table has one or more columns. Aset of columns forms a database record
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Meta Data
Recall that a database is self
describing
Metadata: Data about data
Data that describe how user data are stored interms of table name, column name, data type,
length, primary keys, etc
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Metadata are typically stored in System tables
or System Catalog and are typically only
directly accessible by the DBMS or by the
system administrator. Have a look at theDatabase Documenter feature of MS Access
(under the tools menu, choose Analyze and then
Documenter)
This tool queries the system tables to give all
kinds of Metadata for tables, etc. in an MS
Access database
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Indexes
In keeping with our desire to provide users with
several different views of data, indexes provide
an alternate means of accessing user data.
Sorting and Searching:
An index for our new banking example might
include the account numbers in a sorted order
Indexes allow the database to access a record
without having to search through the entire table
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Updating data requires an extra step: The
index must also be updated
Example:
Index in a book consists of two things:
1) A Keyword stored in order
2) Apointerto the rest of the information. In thecase of the book, the pointer is a page number
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Roles Involve In Integrated Database Environment
Database Administrator
Application Programmers
End-users
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Files ManagementBasic File Operations
The operations possible on a file are:
Open
Close
Save
Save As
Import / Export
Upload / Download
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Files ManagementFile Manipulation Operations
Some operations are used for filemanipulation:
Creation of tables
Insertion of records
Deletion of records
Modification of records
Sorting of records
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Files ManagementTypes Of Files
Data Files - contain only data
Master File - contain relatively permanent recordsthat are periodically updated
Transaction File - a temporary holding file that holds
all changes to be made to the master file
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Files ManagementTypes Of Files
Table Files
Table files are permanent files containing
reference data used when processingtransaction files
Report Files
These are the collected contents of individual
repots or documents produced by the system
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Files Management
Data Processing Methods
Online Processing
Also called real-time processing
Transactions entered into a computer systems asthey take place, and update the master files as the
transactions occur
Storage must be online and fast
May require expensive infrastructure
Used in financial institutions, airline etc
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Files Management
Data Processing Methods
Batch Processing
Data collected over certain period of time in a
transaction file and then processed against a master
file all at one time
Less expensive but slow procedure
Uses offline storage method
Widely used in financial institutions computerized
system