Chapter 1: Introduction

Database System Concepts, 7th Ed.

©Silberschatz, Korth and Sudarshan
See www.db-book.com for conditions on re-use
 Outline

 Database-System Applications
 Purpose of Database Systems
 View of Data
 Database Languages
 Database Design
 Database Engine
 Database Architecture
 Database Users and Administrators
 History of Database Systems

Database System Concepts - 7th Edition 1.2 ©Silberschatz, Korth and Sudarshan
 Files and Databases

 File: A collection of records or documents

dealing with one organization, person, area
or subject. (Rowley)
• Manual (paper) files
• Computer files
 Database: A collection of similar records
with relationships between the records.
(Rowley)
• bibliographic, statistical, business data, images,
etc.

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.3 ©Silberschatz, Korth and Sudarshan
 Difference Between File and Database

SL Feature File Database

1 Definition File is a collection of Database is a collected of

records or documents similar records with
dealing with relationship between records
organizations, person or
subject
2 Redundancy High Low

3 Integrity Harder Ensured via constraints,

primary/foreign keys

4 Scalability Not ideal for larger and Designed for scalability and
complex data performance

5 Searching and Slower, requires custom Fast and powerful using

Filtering logic SQL/queries

Database System Concepts - 7th Edition 1.4 ©Silberschatz, Korth and Sudarshan
 Database

 A Database is a collection of stored operational data used by the application

systems of some particular enterprise. (C.J. Date)
• Paper “Databases”
 Still contain a large portion of the world’s knowledge
• File-Based Data Processing Systems
 Early batch processing of (primarily) business data
 Batch processing was common: data was processed in groups at
scheduled times (e.g., payroll every Friday)
• Database Management Systems (DBMS)

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Database System Concepts - 7th Edition 1.5 ©Silberschatz, Korth and Sudarshan
 Terms and Concepts

 Database Management System -- DBMS

• Software system used to define, create, maintain and provide
controlled access to the database and repository
 Repository
• AKA Data Dictionary
• The place where all metadata for a particular database is stored
• may also include information on relationships between files or tables
in a particular database

IS 257 – Spring 2004

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 Terms and Concepts

 Metadata
• Data about data
 In DBMS means all of the characteristics describing the
attributes of an entity, E.G.:
• name of attribute
• data type of attribute
• size of the attribute
• format or special characteristics
• Characteristics of files or relations
 name, content, notes, etc.

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.7 ©Silberschatz, Korth and Sudarshan
 Why DBMS?

 History
• 50’s and 60’s all applications were custom built for particular needs
• File based
• Many similar/duplicative applications dealing with collections of
business data
• Early DBMS were extensions of programming languages
• 1970 - E.F. Codd and the Relational Model
• 1979 - Ashton-Tate & first Microcomputer DBMS

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.8 ©Silberschatz, Korth and Sudarshan
 File Based Systems

Application File

Delivery Toys
List Addresses

Coal
Estimation Naughty

Just what
asked for Nice Toys

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.9 ©Silberschatz, Korth and Sudarshan
 From File Systems to DBMS

 Problems with File Processing systems

• Inconsistent Data : The same data may be stored in different files but in
different formats or with different values. Effect: Leads to confusion,
duplication, and incorrect results.
• Inflexibility: Making changes (like adding a new field or format) requires
rewriting application programs. Effect: System becomes hard to upgrade or
modify.
• Limited Data Sharing: Data is isolated in separate files for each application.
Effect: Reduces collaboration and efficient use of data.
• Poor enforcement of standards: No centralized control over how data is
stored or named. Effect: Harder to ensure data quality and consistency.
• Excessive program maintenance: When data formats or requirements
change, all related programs must be updated manually. Effect:
Time-consuming, error-prone, and costly to maintain.

IS 257 – Spring 2004

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 Database Systems

 DBMS contains information about a particular enterprise

• Collection of interrelated data
• Set of programs to access the data
• An environment that is both and to use
 Database systems are used to manage collections of data that are:
• Highly valuable
• Relatively large
• Accessed by multiple users and applications, often at the same
time.
 A modern database system is a complex software system whose
task is to manage a large, complex collection of data.
 Databases touch all aspects of our lives

Database System Concepts - 7th Edition 1.11 ©Silberschatz, Korth and Sudarshan
 DBMS Benefits
•Minimal Data Redundancy
Same data is not stored in multiple places unnecessarily, which saves space and avoids
confusion.
•Consistency of Data
Since there's less duplication, data is more likely to be accurate and up to date everywhere it's
used.
•Integration of Data
Data from different departments or systems can be brought together into one database,
allowing a complete view of information.
•Sharing of Data
Multiple users and applications can access the same data simultaneously while ensuring data
security and consistency.
•Ease of Application Development
Developers don’t need to handle data management from scratch; DBMS provides tools and
APIs for easy integration and development.
•Uniform Security, Privacy, and Integrity Controls
Centralized rules and access control protect data from unauthorized access and maintain data
correctness and privacy.
•Data Accessibility and Responsiveness
Data can be retrieved quickly using powerful query languages like SQL, improving the speed
and responsiveness of applications.
•Data Independence
Applications are independent of how data is stored. If the data structure changes, the
application code doesn't necessarily need to change.
•Reduced Program Maintenance
Because data handling is centralized and managed by the DBMS, individual programs require
less maintenance when the database changes.

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.12 ©Silberschatz, Korth and Sudarshan
 Terms and Concepts


• Physical representation and location of data and the use of that data
are separated
 The application doesn’t need to know how or where the
database has stored the data, but just how to ask for it.
 Moving a database from one DBMS to another should not have a
material effect on application program
 Recoding, adding fields, etc. in the database should not affect
applications

IS 257 – Spring 2004

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 Database Environment

CASE User Application

Tools Interface Programs

DBMS
Repository Database

IS 257 – Spring 2004

Database System Concepts - 7th Edition 1.14 ©Silberschatz, Korth and Sudarshan
  Users (with terminals/computers)
• These are end-users or developers who interact with the database system through a User
Interface.
 User Interface
• Acts as a communication bridge between users and the database system.
• Allows users to input queries, commands, and view results.
 CASE Tools (Computer-Aided Software Engineering Tools)
• Software applications that help in database design and management tasks.
• Interact with the Repository (a storage location for metadata, design information, etc.) and
are accessible through the User Interface.
 Application Programs
• Custom programs developed to interact with the database for specific tasks (like payroll,
inventory systems, etc.).
• They interact with both the User Interface and DBMS.
 DBMS (Database Management System)
• The core software that controls the storage, retrieval, and management of data in databases.
• Acts as the intermediary between Application Programs, CASE Tools, Repository, and the
Database itself.

Database System Concepts - 7th Edition 1.15 ©Silberschatz, Korth and Sudarshan
  Repository
• A special database that stores metadata (data about data) — for example, definitions of
tables, fields, relationships, constraints, and system documentation.
 Database
• The actual collection of data that the DBMS manages.
• Stores the operational data for the system (like customer records, transactions, etc.)
.
 How it All Connects:
 Users interact via a User Interface, which communicates with both Application Programs and
CASE Tools.
 CASE Tools interact with the Repository to access metadata.
 Application Programs send and receive data from the DBMS.
 The DBMS manages both the actual Database and the Repository, ensuring data integrity,
security, and consistency.

Database System Concepts - 7th Edition 1.16 ©Silberschatz, Korth and Sudarshan
 Database Components

DBMS
===============
Design tools
Table Creation
Form Creation
Query Creation
Report Creation
Application
Procedural
language Programs
Database
compiler (4GL)
=============
Run time
Database contains: Form processor
User’s Data Query processor User
Metadata Report Writer Interface
Indexes Language Run time
Applications
Application Metadata

IS 257 – Spring 2004

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 Database Applications Examples

 Enterprise Information
• Sales: customers, products, purchases
• Accounting: payments, receipts, assets
• Human Resources: Information about employees, salaries, payroll
taxes.
 Manufacturing: management of production, inventory, orders, supply
chain.
 Banking and finance
• customer information, accounts, loans, and banking transactions.
• Credit card transactions
• Finance: sales and purchases of financial instruments (e.g., stocks
and bonds; storing real-time market data
 Universities: registration, grades

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 Database Applications Examples (Cont.)

 Airlines: reservations, schedules

 Telecommunication: records of calls, texts, and data usage, generating
monthly bills, maintaining balances on prepaid calling cards
 Web-based services
• Online retailers: order tracking, customized recommendations
• Online advertisements
 Document databases
 Navigation systems: For maintaining the locations of varies places of
interest along with the exact routes of roads, train systems, buses, etc.

Database System Concepts - 7th Edition 1.19 ©Silberschatz, Korth and Sudarshan
 Purpose of Database Systems

In the early days, database applications were built directly on top of file
systems, which leads to:

 Data redundancy and inconsistency: data is stored in multiple file

formats resulting induplication 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 - 7th Edition 1.20 ©Silberschatz, Korth and Sudarshan
 Purpose of Database Systems (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
 Ex: 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 - 7th Edition 1.21 ©Silberschatz, Korth and Sudarshan
 University Database Example

 In this text we will be using a university database to illustrate all the

concepts
 Data consists of information about:
• Students
• Instructors
• Classes
 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

Database System Concepts - 7th Edition 1.22 ©Silberschatz, Korth and Sudarshan
 View of Data

 A database system is a collection of interrelated data and a set of

programs that allow users to access and modify these data.
 A major purpose of a database system is to provide users with an
abstract view of the data.
• Data models
 A collection of conceptual tools for describing data, data
relationships, data semantics, and consistency constraints.
• Data abstraction
 Hide the complexity of data structures to represent data in the
database from users through several levels of data abstraction.

Database System Concepts - 7th Edition 1.23 ©Silberschatz, Korth and Sudarshan
 Data Models

 A collection of tools for describing

• Data
• Data relationships
• Data semantics
• Data constraints
 Relational model
 Entity-Relationship data model (mainly for database design)
 Object-based data models (Object-oriented and Object-relational)
 Semi-structured data model (XML)
 Other older models:
• Network model
• Hierarchical model

Database System Concepts - 7th Edition 1.24 ©Silberschatz, Korth and Sudarshan
 Relational Model

 All the data is stored in various tables.

 Example of tabular data in the relational model

Columns

Rows

Ted Codd
Turing Award 1981

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 A Sample Relational Database

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 Levels of Abstraction

 Physical level: describes how a record (e.g., instructor) is stored.

 Logical level: describes data stored in database, and the relationships
among the data.
type = record
: string;
: string;
: string;
: integer;
end;
 View level: application programs hide details of data types. Views can
also hide information (such as an employee’s salary) for security
purposes.

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 View of Data

An architecture for a database system

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 Instances and Schemas

 Similar to types and variables in programming languages

 Logical Schema – the overall logical structure of the database
• Example: The database consists of information about a set of
customers and accounts in a bank and the relationship between
them
 Analogous to type information of a variable in a program
 Physical schema – the overall physical structure of the database
 Instance – the actual content of the database at a particular point in
time
• Analogous to the value of a variable

Database System Concepts - 7th Edition 1.29 ©Silberschatz, Korth and Sudarshan
 Physical Data Independence

 Physical Data Independence – the ability to modify the physical

schema without changing the logical schema
• Applications depend on the logical schema
• In general, the interfaces between the various levels and
components should be well defined so that changes in some parts
do not seriously influence others.

Database System Concepts - 7th Edition 1.30 ©Silberschatz, Korth and Sudarshan
 Data Definition Language (DDL)

 Specification notation for defining the database schema

Example: create table (
char(5),
varchar(20),
varchar(20),
numeric(8,2))
 DDL compiler generates a set of table templates stored in a

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

• Database schema
• Integrity constraints
 Primary key (ID uniquely identifies instructors)
• Authorization
 Who can access what

Database System Concepts - 7th Edition 1.31 ©Silberschatz, Korth and Sudarshan
 Data Manipulation Language (DML)

 Language for accessing and updating the data organized by the

appropriate data model
• DML also known as query language
 There are basically two types of data-manipulation language
• Procedural DML -- require a user to specify what data are
needed and how to get those data.
• Declarative DML -- require a user to specify what data are
needed without specifying how to get those data.
 Declarative DMLs are usually easier to learn and use than are
procedural DMLs.
 Declarative DMLs are also referred to as non-procedural DMLs
 The portion of a DML that involves information retrieval is called a
query language.

Database System Concepts - 7th Edition 1.32 ©Silberschatz, Korth and Sudarshan
 SQL Query Language

 SQL query language is nonprocedural. A query takes as input several

tables (possibly only one) and always returns a single table.
 Example to find all instructors in Comp. Sci. dept
select
from
where 'Comp. Sci.'
 SQL is NOT a Turing machine equivalent language
 To be able to compute complex functions SQL is usually embedded in
some higher-level language
 Application programs generally access databases through one of
• Language extensions to allow embedded SQL
• Application program interface (e.g., ODBC/JDBC) which allow SQL
queries to be sent to a database

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 Database Access from Application Program

 Non-procedural query languages such as SQL are not as powerful as a

universal Turing machine.
 SQL does not support actions such as input from users, output to
displays, or communication over the network.
 Such computations and actions must be written in a host language,
such as C/C++, Java or Python, with embedded SQL queries that
access the data in the database.
 Application programs -- are programs that are used to interact with
the database in this fashion.

Database System Concepts - 7th Edition 1.34 ©Silberschatz, Korth and Sudarshan
 Database Design

The process of designing the general structure of the database:

 Logical Design – Deciding on the database schema. Database design

requires that we find a “good” collection of relation schemas.
• Business decision – What attributes should we record in the
database?
• Computer Science decision – What relation schemas should we
have and how should the attributes be distributed among the
various relation schemas?
 Physical Design – Deciding on the physical layout of the database

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 Database Engine

 A database system is partitioned into modules that deal with each of

the responsibilities of the overall system.
 The functional components of a database system can be divided into
• The storage manager,
• The query processor component,
• The transaction management component.

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 Storage Manager

 A program module that provides the interface between the low-level

data stored in the database and the application programs and queries
submitted to the system.
 The storage manager is responsible to the following tasks:
• Interaction with the OS file manager
• Efficient storing, retrieving and updating of data
 The storage manager components include:
• Authorization and integrity manager
• Transaction manager
• File manager
• Buffer manager

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 Storage Manager (Cont.)

 The storage manager implements several data structures as part of the

physical system implementation:
• Data files -- store the database itself
• Data dictionary -- stores metadata about the structure of the
database, in particular the schema of the database.
• Indices -- can provide fast access to data items. A database index
provides pointers to those data items that hold a particular value.

Database System Concepts - 7th Edition 1.38 ©Silberschatz, Korth and Sudarshan
 Query Processor

 The query processor components include:

• DDL interpreter -- interprets DDL statements and records the
definitions in the data dictionary.
• DML compiler -- translates DML statements in a query language
into an evaluation plan consisting of low-level instructions that the
query evaluation engine understands.
 The DML compiler performs query optimization; that is, it picks
the lowest cost evaluation plan from among the various
alternatives.
• Query evaluation engine -- executes low-level instructions
generated by the DML compiler.

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 Query Processing

1. Parsing and translation

2. Optimization
3. Evaluation

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 Transaction Management

 A transaction is a collection of operations that performs a single logical

function in a database application
 Transaction-management component ensures that the database
remains in a consistent (correct) state despite system failures (e.g.,
power failures and operating system crashes) and transaction failures.
 Concurrency-control manager controls the interaction among the
concurrent transactions, to ensure the consistency of the database.

Database System Concepts - 7th Edition 1.41 ©Silberschatz, Korth and Sudarshan
 Database Architecture

 Centralized databases
• One to a few cores, shared memory
 Client-server,
• One server machine executes work on behalf of multiple client
machines.
 Parallel databases
• Many core shared memory
• Shared disk
• Shared nothing
 Distributed databases
• Geographical distribution
• Schema/data heterogeneity

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 Database Architecture
(Centralized/Shared-Memory)

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 Database Applications

Database applications are usually partitioned into two or three parts

 Two-tier architecture -- the application resides at the client

machine, where it invokes database system functionality at the
server machine
 Three-tier architecture -- the client machine acts as a front end and
does not contain any direct database calls.
• The client end communicates with an application server, usually
through a forms interface.
• The application server in turn communicates with a database
system to access data.

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 Two-tier and three-tier architectures

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 Database Users

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 Database Administrator

A person who has central control over the system is called a database
administrator (DBA). Functions of a DBA include:

 Schema definition
 Storage structure and access-method definition
 Schema and physical-organization modification
 Granting of authorization for data access
 Routine maintenance
 Periodically backing up the database
 Ensuring that enough free disk space is available for normal
operations, and upgrading disk space as required
 Monitoring jobs running on the database

Database System Concepts - 7th Edition 1.47 ©Silberschatz, Korth and Sudarshan
 History of Database Systems

 1950s and early 1960s:

• Data processing using magnetic tapes for storage
 Tapes provided only sequential access
• Punched cards for input
 Late 1960s and 1970s:
• Hard disks allowed direct access to data
• Network and hierarchical data models in widespread use
• Ted Codd defines the relational data model
 Would win the ACM Turing Award for this work
 IBM Research begins System R prototype
 UC Berkeley (Michael Stonebraker) begins Ingres prototype
 Oracle releases first commercial relational database
• High-performance (for the era) transaction processing

Database System Concepts - 7th Edition 1.48 ©Silberschatz, Korth and Sudarshan
 History of Database Systems (Cont.)

 1980s:
• Research relational prototypes evolve into commercial systems
 SQL becomes industrial standard
• Parallel and distributed database systems
 Wisconsin, IBM, Teradata
• Object-oriented database systems
 1990s:
• Large decision support and data-mining applications
• Large multi-terabyte data warehouses
• Emergence of Web commerce

Database System Concepts - 7th Edition 1.49 ©Silberschatz, Korth and Sudarshan
 History of Database Systems (Cont.)

 2000s
• Big data storage systems
 Google BigTable, Yahoo PNuts, Amazon,
 “NoSQL” systems.
• Big data analysis: beyond SQL
 Map reduce and friends
 2010s
• SQL reloaded
 SQL front end to Map Reduce systems
 Massively parallel database systems
 Multi-core main-memory databases

Database System Concepts - 7th Edition 1.50 ©Silberschatz, Korth and Sudarshan
 End of Chapter 1

Database System Concepts - 7th Edition 1.51 ©Silberschatz, Korth and Sudarshan