Lecture 3 History of Database File System

8/14/2019 Lecture 3 History of Database File System

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DBMS

Lecture 3

History of DatabaseFile System

3 Levels of Abstraction

Types of DatabasesComponents of DBMS

Hitesh Mahapatra


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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'sThe 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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Before we have DBMS

Before we have DBMS

UserInventory

Control

Applications DataFiles

UserCustomer

Order

Question: When a customer ordered 10 PC

monitors, how many files do you have to update? Key issues: data sharing,

data redundancy


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A Simple Architecture

A Simple Architecture

SQL

C/C++

Programs

DBMS

ApplicationsDatabases

Shared facilities:Backup and recoveryData 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 to

data 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 caused by 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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Disadvantages of Database Approach

DBMS has High initial cost

DBMS has High Overhead - requirespowerful computers

DBMS are not special purpose softwareprograms e.g., contrast an accountingsoftware package like Quicken orPeachTree with DBMS like MS Access

Additional expertise required


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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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view 1 view 2 ..... view n

Logical

view

Physical

view

Payroll Inventory Sales

Companydatabase

Filesondisks

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, andthe relationships 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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DatabasesTypes & Physical Locations

Shared Databases

Shared by users in an organization within onelocation

Typically found on local-area networks


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Databases

Types & Physical LocationsDistributed 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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Database Administrator (DBA)

The person who co-ordinates all relatedactivities 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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Contents of a Database

A Database contains:

User Data

Metadata

Indexes


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User Data

Data users work with directly by entering,

updating and viewing

For our purposes, data will be generally stored

in tables with some relationships between tables

Each table has one or more columns. A set 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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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

Print

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 processing

transaction 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

Documents

Lecture 3 History of Database File System