Database Management Unit-I

8/13/2019 Database Management Unit-I

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UNIT

I

Introduction to Database Systems

DATABASE MANAGEMENT SYSTEMS


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Terminology

Data = known facts that can be recorded

Database (DB) = logically coherent collection of related data with some inherent

meaning

Entities such as students, courses, sections

Relationships between entities such as students taking courses and sections

being part of courses

Database management system (DBMS) = collection of programs that enable

users to create and maintain a DB; general-purpose software system that

facilitates process of defining, constructing, and manipulatingDBs for various

applications.


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A shared collection of logically related data and a description of this

data, designed to meet the information needs of an organization

Data repository (data resource)

Designed independently of applications (i.e., data abstraction)

Long-term information needs at the enterprise level

Primarily designed for quick and efficient data retrieval

What is database?


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What the Purpose for Learning about Database?

Paradigm shift: Data driven business environment

Customer information (e.g.,

database marketing, CRM)

Competitor andmarketplace information

Production efficienciesKnowledge and innovation

(e.g., knowledge

management, businessintelligence)

Coordination of vendors (e.g.,supply chain management


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History (1)

Early 60s

Charles Bachman introduced first general purpose DBMS known as IDS (TuringAward 1973) at General Electric (GE)

Integrated Data Store (IDS) formed the basis for N/w data model

Network Data Model was standardized by the Conference on Data SystemsLanguages (CODASYL).

Late 60s

IBM developed IMS

Information Management Systems (IMS) formed basis for Hierarchical DataModel

Hierarchichal Data Model

SABRE system for making airline reservation jointly by IBM and American

Airlines (allowed several people to access the same data thro computer N/W) 70s

Edgar Codd, at IBM proposed Relational Data Model (Turing Award 1981)

Use of DBMSs for managing corporate data became standard practice


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History (2)

80s

Relational Data Model became dominant DBMS paradigm

SQL query language for relational DBs developed as part of IBMs System R

projectis now the standard query language

Transaction Management (concurrent execution of db programs) (James Gray,

Turing Award 1999)

Now Object-oriented Data Model

Data warehouse and data mining

Accessing databases through the web/internet

Multimedia data

Text data (information retrieval)

Structure of the data (XML)


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Traditional File-Based System

Definition:

"A collection of application programs that perform services for the end-userssuch as the production of reports. Each program defines and manages its

own data."

PayrollOperating

expenses

Customer

transactionsVendorsInventory

Program Program Program Program Program

Report Report Report Report Report

One fi le, one application


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Data Redundancy

Customer Order File

Invoice number

Customer account number

Customer name, address, city, state, zip code

Order date

Product code, product description, price, unit

Customer Account File

Account Number

Customer name, mailing address, city, state, zip code

Customer Mailing List File

Customer name, mailing address, city, state, zip code


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File-Based Systems

Records contain logically related data

Limitations:

Separation and isolation of data (one file, one program)

Duplication of data Loss of data integrity - uncertainty of the correctversion of data and no

consistency

Data dependence - application program defines the data

Incompatibility of file formats

Fixed queries/proliferation of application programs - little flexibility inmeeting changing information needs


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Database

Data and

DataDefinitions

Applications

A shared collection of logically related data (and a description of this

data), designed to meet the information needs of an organization.

SeparationCentral Repository


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Data Abstraction

Separation between the datas structure (definition) and the application

programs

Data andData

Definitions

Applications

CentralRepository

DBMS

Application programs can be runon either the clients or server


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Organizing Data

Entity - distinct object (i.e., person, place, thing, concept or event)

Attribute - describes some aspect of the entity (object)

Property of the entity

Relationship - association between entities

Customers

Account_number

NameAddress

Purchases

Invoice_number

Account_numberPurchase_date

Attributes

Relationship

Entity Entity


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Database

Customer

OrdersOrder Items

Manufacturers

Products

DBMS

Management

Queries

ApplicationPrograms

Other

Software

DDL

DML

Controlled accessCentral Repository

(Organizational resource) Single Access Point Multitude of

Applications


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Advantages of the Database Approach

Control of data redundancy

Data consistency

Efficient data access, Greater informational gain, more information from the

same amount of data

Sharing data, organizational resource (i.e., shared resource)

Improved data integrity, validity and consistency

Improved access and security

Enforcement of standards

Concurrency Access and Crash recovery

Data Administration

Reduced Application development time


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Database Applications

Traditional database applications (banks, library catalogs, inventory, airlines,

universities)

Multimedia databases (images)

Geographic information systems

Data warehouse and online analytical processing (OLAP)

Real time and active database technology (sensor systems, safety-critical

systems)

World wide web (e-commerce, internet banking)


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DBMS Available

ORACLE

DB2by the IBM

MS-SQL

Teradata

Sybase

Informix


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Data Model

Collection of high level data description constructs that hide many low-levelstorage details

Semantic data model

More abstract, high level data model (makes it easier to describe about the data)

Widely used one is ER modelpictorially denotes entities and relationshipsamong them

Relational Model Relationset of records

Schema

A description of data in terms of a data model is schema

Schema for a relation specifies its name, name of each field (or attribute or

column) and type of each field. Example

Students(sid: string, name: string, login: string, gpa: real)

Each row in the relation is a record that describes the student


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Other Data Models

Relational Data model ( dominant model)

Hierarchical data model

Network model

Objectoriented model

Objectrelational model


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Types of Database Models

HIERARCHICAL

RELATIONAL

TABLEROW

COLUMN

VALUE


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Database Architecture/ Levels of Data Abstractions

Internal level

(storage view)

Conceptual level(community user view)

External level(individual user

views)

Database


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Conceptual Schema

Describes data in terms of the data model of the DBMS.

In a RDBMs, the conceptual schema describes all relations that are stored in the

database. Eg. University Db

Students (sid: string, name: string, gpa: real)

Faculty (fid: string, fname: string, sal: real)

Physical schema Specifies additional storage details

Summarizes how the relations described in conceptual schema are actually stored

on secondary storage devices like disks and tapes

Decide on what file organizations to use to store relations and indexes to speed

up data retrieval operations

External Schema

Allow data access to be customized at the level of individual users or groups of

users.


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An Example of the Three Levels

SNo FName LName Age Salary

SNo FName LName Age Salary

SNo LName BranchNo

struct STAFF {

int staffNo;

int branchNo;

char fName[15];char lName[15];

struct date dateOfBirth;

float salary;

struct STAFF *next;

/* pointer to next Staff record

*/};

index staffNo; index branchNo;

/* define indexes for staff */

BranchNo

Conceptual View

External View1

Internal View

External View2


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Database Design Phases

DATA ANALYSIS

Entities - Attributes - Relationships - Integrity Rules

LOGICAL DESIGN

Tables - Columns - Primary Keys - Foreign Keys

PHYSICAL DESIGN

DDL for Tablespaces, Tables, Indexes


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Data Independence

Ability to change one schema level without affecting the higher levelschemas

Physical Data Independence

Ability to change physical schema or internal schema without affecting

conceptual or logical schema

Logical Data Independence

Ability to change logical schema without affecting External or view schema.

(application programs)

One imp. Adv of DBMS is data independence


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Characteristics of the DB approach (1)

Single repository of data defined once, maintained and accessed by users

Self-describing nature of DB

DB + description of DB structures and constraints

stored in primary DB metadata (stored in catalog)

DBMS software works with any number of DB applications

Insulation between programs and data, and data abstraction

Program--data independence Program--operation independence (OO DBMS)

Abstraction: conceptual representation of data, no details of how data is stored

or operators are implemented


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Characteristics of the DB approach (2)

Data model

Relational data model

Object-oriented data model

Entity-relationship data model

Support multiple views of data

view = subset of DB

virtual data derived from DB (not explicitly stored)

Sharing data and multi-user transaction processing

Concurrency control

Online transaction processing (OLTP)


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Query Languages

Query questions involving data stored in dbms

Relational Algebra

formal query language based on collection of operators for manipulating

relations

Relational Calculus

formal query language based on mathematical logic

DDL: Data Definition Language

Defines db structure

Commands used are for creating, altering, query data

DML: Data Manipulation Language For manipulating (inserting, deleting, updating) db contents

Procedural and Nonprocedural (Declarative) DML


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Types of DML

Procedural DML Must be embedded in a programming language. Searches for and retrieves

individual db records and uses looping and other constructs of the host

programming language to retrieve multiple records

Non-Procedural or Declarative DML Can be used as a stand-alone query language or can be embedded in a

programming language. Searches for and retrieves information from

multiple related db records in a single command


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Components of a Database Environment

Hardware

Software: DBMS, application program and query software

Data: Organized in a schema, partitioned into subschemas

Procedures: Govern the design, access and use of the database

People: Administrators (DA, DBA), designers (logical and physical),

application developers and users (novice and high-powered)


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Database System

Stored Data Defn.Stored Database

Software to access stored data

Software to process queries/programs

DBMS

Software

Application Programs/Queries

Users

DATABASE

SYSTEM

(META-DATA).


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Users of the Database

Day-to-day use of the DB

Database administrators (DBA)

Database designers

End-users

Casual end-users

Nave or parametric users

Sophisticated end-users

Stand-alone users

System analysts and application programmers (software engineering)


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Implications of the DB approach

Potential for enforcing standard

Reduce application development time

Flexibility

Availability of up-to-date info


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When not to use a DBMS

Unnecessary overhead costs Security, concurrency control, recovery and integrity

High initial investment in hardware, software, training

DB and applications are simple, well defined, not expected to change

Real-time requirements not met (due to overhead)

Multi-user access not required

Database Management Unit-I

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