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Data Base Organization
and File Structure
— Chapter 1 —
Suresh Choubey, Ph.D.
May 22, 2017
Data Base Organization and File
Structure: Introduction
1
Chapter 1: Introduction

What is a data database?

A database is a collection of very large integrated
collection of related data

Data are facts about people, event and other
entities that can be recorded and that have implicit
meaning, e.g., name, address and telephone # of
all people we know
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Characteristics of a database?

A database is logically coherent collection of data
with some inherent meaning

A database is designed, built and populated with
data for a specific purpose

A database represents some aspect of real world,
called mini world (models real world enterprise)

May 22, 2017
Entities, relationship
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

What is a database management system?

Database management systems (DBMS) is a
collection of programs that enables users to create
(store) and maintain a database. It involves design,
construction (storage of data) and manipulation

May 22, 2017
Database systems = DBMS + database
Data Base Organization and File
Structure: Introduction
4
Chapter 1: Introduction

Characteristics of database approach

Self-contained nature of database systems

Data + meta data + constraints on data are stored together in
system catalog


Application programs are independent of data
Insulation between programs and data
May 22, 2017

DBMS access programs are independent of files

This property is called program-data independence
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Characteristics of database approach(Cont. ….)

Data abstraction:DBMS gives conceptual representation
of data, e.g. data model

Support of multiple views of data
May 22, 2017

Different users have differing views of database

Virtual data can be derived
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Intended use of DBMS approach

Controlled redundancy

Redundancy causes duplication of efforts, wastage of storage
space and inconsistency

Controlled redundancy may be useful in saving access time as
some controlled data are stored at more than one place

Sharing of data:

May 22, 2017
Requires concurrency control measures
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Intended use of DBMS approach (Cont. ….)

Restricting unauthorized access


DBMS provides security and authorization subsystems
Providing multiple interfaces

Query language for casual users, programming language for
application programmers, forms for pragmatic users, menu
driven interfaces for native users and natural language
interfaces
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Intended use of DBMS approach (Cont. ….)

Representing complex relationships among data

Enforcing Integrity constraints

Providing backup and Recovery from crashes

Potential for enforcing standards

Flexibility – can add changes in mini world

Reduced application development time
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Intended use of DBMS approach (Cont. ….)

Availability of up-to-date information

Economics of scale


Permits consolidation of data and application
Uniform data administration
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Disadvantages of DBMS approach

High cost due to high initial investment for h/w and s/w
and incorporation of sub-systems for security,
concurrency control, recovery and integrity function

Security Problems

Initial development time
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

File Vs databases (Slide from text book author)

Application must stage large datasets between main memory and
secondary storage (e.g., buffering, page-oriented access, 32-bit
addressing, etc.)

Special code for different queries

Must protect data from inconsistency due to multiple concurrent
users

Crash recovery

Security and access control
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Why study databases ? (Slide from text book author)

Shift from computation to information


at the “low end”: scramble to webspace (a mess!)

at the “high end”: scientific applications
Datasets increasing in diversity and volume

Digital libraries, interactive video, Human Genome project, EOS
project

May 22, 2017
... need for DBMS exploding
Data Base Organization and File
Structure: Introduction
13
Chapter 1: Introduction

Why study databases ? (Slide from text book
author)

DBMS encompasses most of CS

May 22, 2017
OS, languages, theory, “A”I, multimedia, logic
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Personnel

DBA – responsible for database and DBMS, account
allocation, security maintenance


Database designers

Identify data and design data structures

Identify views and combine them
DBMS designers and implementers
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Introduction

Personnel (Cont. ….)

End users – access database for querying, updating and
generating reports

Casual end users

Naïve or parametric end users – use canned transactions

Sophisticated end users

Tool developers

Operators and maintenance personnel
May 22, 2017
Data Base Organization and File
Structure: Introduction
16
Chapter 1: Introduction

DBMS can be network, relational, hierarchical and
others

DBMS can also be single-user or multi-user

DBMS can be centralized or distributed (DDBMS)

homogeneous(use same DBMS s/w at multiple sites)

Heterogeneous (use s/w to access several
autonomous pre-existing database)
May 22, 2017
Data Base Organization and File
Structure: Introduction
17
Chapter 1: Introduction

Data Models

Is a set of concepts that describes the structure of the
database (i.e., data types, relationship and constraints
that should hold on data)

Is a set of operators for specifying retrievals and
updates on database

Provides abstraction
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models

A schema is a description of a particular collection of
data, using the a given data model

The relational model of data is the most widely used
model today

Main concept: relation, basically a table with rows and
columns

Every relation has a schema, which describes the columns, or
fields
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models: Cocepts


High level called object based models

Entity - is an object hat is represented in the database

Attribute – is a property that describes some aspects of object

Relationship
Implementation Level – record-based data models such as relational and
network

Physical data models – describes how data is stored in the computer by
representing information such as record formats, record orderings and
access path
May 22, 2017
Data Base Organization and File
Structure: Introduction
20
Chapter 1: Data Models
Database Schemas:Is the description of database. Schema
diagrams are used to represent it. Schema diagram
consists of schema construct. e.g., Student
Name
StudName
Class

It does not change frequently

Called INTENSION
Major
Database Instance: Data in database at a particular time or
occurrence or state
called EXTENSION
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: DBMS Architecture
(Three schema or ANSI-SPARC)
External view - 1
External View - n
External level
or view level
External/Conceptual mapping
Conceptual Schema
Conceptual level
Conceptual/Internal mapping
Internal Schema
Internal level
Stored database
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models

Many views, single conceptual (logical) schema and
physical schema

External View: contains n view, each view schema describing view
of one user

Conceptual View: describes structure of whole database for a
community of users

Internal View: describes physical storage structure of database

Provides abstraction
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models

Mapping: required to map user’s request to conceptual
to internal to stored database and then back after
formatting it to suit the user’s view of database

Data Independence: Capacity to change the conceptual
schema without having to change external schema or
application programs

May 22, 2017
Applications insulated from how data is structured and stored
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models

Logical Data Independence: Protection from
changes in logical structure of data

Physical Data Independence: Protection from
changes in physical structure of data
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: Data Models

Physical Data Independence: Physical data independence
– capacity to change the internal schema without having to
change the conceptual (or external) schema

Change to reorganize physical files by creating additional access
structures

Mapping information is stored in catalog

Disadvantages: Overhead when compiling or executing a
query or program  inefficiency in DBMS
May 22, 2017
Data Base Organization and File
Structure: Introduction
26
Chapter 1: Data Models


Example: University Database
Conceptual schema:
Students(sid: string, name: string, login: string, age: integer,
gpa:real)
Courses(cid: string, cname:string, credits:integer)
Enrolled(sid:string, cid:string, grade:string)


Physical schema:

Relations stored as unordered files

Index on first column of Students
External Schema (View):

May 22, 2017
Course_info(cid:string,enrollment:integer)
Data Base Organization and File
Structure: Introduction
27
Chapter 1: DBMS Languages

DDL: can be used to define conceptual and internal schema
in DBMS, where there is no strict separation

DDL is used to specify conceptual and SDL to specify internal where
there is separation

VDL: is used to specify user views and their mapping to
conceptual

VDL statements can be compiled separately or can be imbedded in a
programming language
May 22, 2017
Data Base Organization and File
Structure: Introduction
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Chapter 1: DBMS Languages

DML: is used for retrieval, insertion, deletion and
modification of data


May 22, 2017
High level or non-procedural DML

Can be used to specify complex database operation

Called set-at-a-time or set oriented DML
Low level or procedural DML

Embedded in a general-purpose programming language

Called record-at-a-time DML
Data Base Organization and File
Structure: Introduction
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Chapter 1: DBMS Languages

DML: is declarative as it set what to retrieve and not how to
retrieve


When DML is embedded in a programming language

DML is called data sub-language

Programming language is called host language
DML standalone is called Query Language
May 22, 2017
Data Base Organization and File
Structure: Introduction
30
DBMS architecture



A typical DBMS has a
layered architecture
The figure does not
show the concurrency
control and recovery
components
This is one of several
possible architectures;
each system has its
own variations
May 22, 2017
(Slide from text book author)
Query Optimization
and Execution
Relational Operators
These layers
must consider
concurrency
control and
recovery
Files and Access Methods
Buffer Management
Disk Space Management
DB
Data Base Organization and File
Structure: Introduction
31
Chapter 1: Summary
(Slide from text book author)

DBMS used to maintain, query large datasets.

Benefits include recovery from system crashes, concurrent
access, quick application development, data integrity and
security

Levels of abstraction give data independence

A DBMS typically has a layered architecture

DBAs hold responsible jobs and are well-paid

DBMS R&D is one of the broadest, most exciting areas in CS
May 22, 2017
Data Base Organization and File
Structure: Introduction
32