Database System Concepts Essay example

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Chapter 1: Introduction

Database System Concepts, 6th Ed.
©Silberschatz, Korth and Sudarshan
See www.db­ for conditions on re­use

Database Management System (DBMS)
 DBMS contains information about a particular enterprise

Collection of interrelated data

Set of programs to access the data

An environment that is both convenient and efficient to use

 Database Applications:

Banking: transactions

Airlines: reservations, schedules

Universities: registration, grades

Sales: customers, products, purchases

Online retailers: order tracking, customized recommendations

Manufacturing: production, inventory, orders, supply chain

Human resources: employee records, salaries, tax deductions

 Databases can be very large.
 Databases touch all aspects of our lives
Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

University Database Example
 Application program examples

Add new students, instructors, and courses

Register students for courses, and generate class rosters

Assign grades to students, compute grade point averages (GPA) and generate transcripts

 In the early days, database applications were built directly on top of

file systems

Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

Drawbacks of using file systems to store data

Data redundancy and inconsistency

Multiple file formats, duplication of information in different files

Difficulty in accessing data

Need to write a new program to carry out each new task

Data isolation — multiple files and formats

Integrity problems

Integrity constraints (e.g., account balance > 0) become
“buried” in program code rather than being stated explicitly

Hard to add new constraints or change existing ones

Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

Drawbacks of using file systems to store data (Cont.)

Atomicity of updates

Failures may leave database in an inconsistent state with partial updates carried out

Example: Transfer of funds from one account to another should either complete or not happen at all

Concurrent access by multiple users

Concurrent access needed for performance

Uncontrolled concurrent accesses can lead to inconsistencies
– Example: Two people reading a balance (say 100) and updating it by withdrawing money (say 50 each) at the same time

Security problems

Hard to provide user access to some, but not all, data

Database systems offer solutions to all the above problems

Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

Data Models
 A collection of tools for describing

 Data relationships
 Data semantics
 Data constraints

 Relational model
 Entity­Relationship data model (mainly for database design)
 Object­based data models (Object­oriented and Object­relational)
 Semistructured data model (XML)
 Other older models:

Network model
Hierarchical model

Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

Relational Model
 Relational model (Chapter 2)
 Example of tabular data in the relational model



Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

A Sample Relational Database

Database System Concepts ­ 6th Edition


©Silberschatz, Korth and Sudarshan

Data Definition Language (DDL)

Specification notation for defining the database schema
create table instructor ( ID char(5), name varchar(20), dept_name varchar(20), salary numeric(8,2))

DDL compiler generates a set of table templates stored in a data dictionary

Data dictionary contains metadata (i.e., data about data)

Database schema

Integrity constraints

Primary key (ID uniquely