Transcript Chapter 3 - Marshall University Personal Web Pages

Chapter 3
The Database Management
System Concept
Fundamentals of Database Management Systems,
2nd ed
by
Mark L. Gillenson, Ph.D.
University of Memphis
John Wiley & Sons, Inc.
Chapter Objectives

Discuss the problems encountered in a
nondatabase information systems
environment.

Discuss the nature of data.

Define data-related terms such as entity
and attribute.
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Chapter Objectives

Define storage-related terms such as field,
record, and file.

Identify the four basic operations
performed on stored data.

Compare sequential access of data with
direct access of data.
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Chapter Objectives

List the five basic principles of the
database concept.

Describe how data can be considered to
be a manageable resource.
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Chapter Objectives

List the three problems created by data
redundancy.

Describe the nature of data redundancy
among many files.

Explain the relationship between data
integration and data redundancy in one
file.
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Chapter Objectives

State the primary defining feature of a
database management system.

Explain why the ability to store multiple
relationships is an important feature of the
database approach.
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Chapter Objectives

Explain why providing support for such
control issues as data security, backup
and recovery, and concurrency is an
important feature of the database
approach.

Explain why providing support for data
independence is an important feature of
the database approach.
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Data Processing Systems

Data was stored in different formats in different
files.

Data was often not shared among different
programs that needed it, necessitating the
duplication of data in redundant files.

Little was understood about file design, resulting
in redundant data within individual files.
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Data Processing Systems

Files often could not be rebuilt after being
damaged by a software error or a
hardware failure.

Data was not secure and was vulnerable
to theft or malicious mischief by people
inside or outside of the company.
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Data Processing Systems

Programs were usually written in such a
manner that if the way that the data was
stored changed, the program had to be
modified to continue working.

Changes in everything from access
methods to tax tables required
programming changes.
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Data Before Database Management
Records and Files

Entity - a “thing” or “object” in our environment
that we want to keep track of.

Entity set - A collection of entities of the same
type (e.g., all of the company’s employees).
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Records and Files

Attribute - a property of, a characteristic of, or a
fact that we know about an entity.

Some attributes have unique values within an
entity set.
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Records and Files
key
field

Record - each row of a structure like above

Fields - the columns, representing the facts

File - the entire structure
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Records and Files

Record type - a structural description of each and
every record in the file

Record occurrence / Record instance - a specific
record of the salesperson file
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Retrieving and Manipulating
Data

Four fundamental operations can be performed on
stored data:

Retrieve or Read - looking at a record’s contents without
changing it

Insert - adding a new record to the file, as when a new
salesperson is hired

Delete - deleting a record from the file, as when a salesperson
leaves the company

Update - changing one or more of a record’s field values
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Data Retrieval Method

Sequential access - the retrieval of all or a
portion of the records of a file one after another,
in some sequence, starting from the beginning,
until all of the required records have been
retrieved.

Physical sequential access - records are retrieved,
one after the other, just as they are stored on the disk
device.

Logical sequential access - records are retrieved in
an order based on the values of one or a combination
of the fields.
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Data Retrieval Method

Direct Access - the retrieval of a single record of
a file or a subset of the records of a file based on
one or more values of a field or a combination of
fields in the file.

a crucial concept in information systems today

requires hardware storage device that will
accommodate direct access

requires software that will take advantage of the
hardware’s capabilities and store and retrieve the
data in such a way that it accomplishes direct access.
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The Database Concept

1. Data as a Manageable Resource

2. Data Integration and Data Redundancy

3. Multiple Relationships

4. Data Control Issues

5. Data Independence
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The Database Concept

Data as a Manageable Resource - The
creation of a data-centric environment in
which a company’s data can truly be
thought of as a significant corporate
resource. A key feature of this
environment is the ability to share data
among those inside and outside of the
company who require access to it.
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The Database Concept

Data Integration and Data Redundancy - The
ability to achieve data integration while at the
same time storing data in a nonredundant
fashion. This, alone, is the central, defining
feature of the database approach.

Multiple Relationships - The ability to store data
representing entities involved in multiple
relationships without introducing data
redundancy or other structural problems.
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The Database Concept

Data Control Issues - The establishment of
an environment that manages certain data
control issues, such as data security,
backup and recovery, and concurrency
control.

Data Independence - The establishment of
an environment that permits a high degree
of data independence.
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Data as a Manageable
Resource

Information systems environment:
 Hardware
 Networks
 Applications
software
 Systems software
 People
 Data
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Data as a Manageable
Resource

Historically, data has not been the highest
priority concern.

As the operational, tactical, and strategic
corporate levels became more dependent
on information systems, data increasingly
became recognized as an important
corporate resource.
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Data as a Manageable
Resource

The corporate community became
increasingly convinced that a firm’s data
could provide a significant competitive
advantage to the firm.

It became clear that data would have to be
managed in an organized way.
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Data as a Manageable
Resource
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Data as a Manageable
Resource

Needed a software utility that could
manage and protect data.

Data could be a critical corporate
resource.

Out of this need was born the database
management system.
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Data as a Manageable
Resource

Reengineering - data is aggressively used
to redesign business processes.

Electronic commerce - a database at the
heart of every web site; allows companies
and customers to conduct business.

ERP systems - collections of application
programs build around a central database.
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Data Integration and Data
Redundancy

Data integration - the ability to tie together
pieces of related data within an
information system.

Data redundancy - the same fact about the
business environment is stored more than
once within an information system.
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Data Redundancy - Problems

Redundant data takes up a great deal of
extra disk space.

If the redundant data has to be updated, it
takes additional time to do so. This can be
a major performance issue.

There is the potential for data integrity
problems.
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Data Integrity

Refers to the accuracy of the data.

Inaccurate data leaves the whole
information system of limited value.
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Data Redundancy,
Data Integrity

When all copies of redundant data are not
updated consistently, a data integrity problem
exists.
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Three Files with Redundant
Data
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Three Files with a Data
Integrity Problem
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
General
Hardware
Company
Files
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General Hardware Company
Combined File
Customer
Number
Customer
Name
Salesperson
Number
HQ City
Salesperson
Number
Salesperson
Name
Commission
%
Year
of
Hire
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Anomalies

Typically occur in poorly structured files.

Problems arise when two different kinds of
data, like salesperson and customer data
are merged into one file.
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Anomalies

Deletion Anomaly - e.g, if you delete a customer and that
record was the only one for a salesperson, the
salesperson’s data is gone.

Insertion Anomaly - e.g., General Hardware cannot add
data about a new salesperson the company just hired
until she is assigned at least one customer.

Update Anomaly - redundant data in the database file
must be updated each place it exists when it changes.
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Database Management
System

A software utility for storing and retrieving
data that gives the end-user the
impression that the data is well integrated
even though the data can be stored with
no redundancy at all.
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Multiple Relationships Horizontal Solution
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Multiple Relationships Vertical Solution
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Data Control Issues

Data security

Backup and Recovery

Concurrency Control
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Computer Security

A very broad topic
 Protecting the physical hardware
environment
 Defending against hacker attacks
 Encrypting data transmitted over networks
 Educating employees on the importance of
protecting the company’s data
 … and many more
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Backup and Recovery

Data can be lost or corrupted in any of a
variety of ways:
a
disaster such as a fire, a hurricane, or an
earthquake
 hackers
 computer viruses
 poorly written application programs
 unintentional error
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Concurrency Problem

Updates to a database can interfere with
each other in such a way that the resulting
data values will be incorrect.

A database management system must be
designed to protect its databases from
such an eventuality.
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Data Independence

Data Dependence - if for any reason the storage
characteristics of the data had to be changed,
the application program itself had to be modified,
often extensively.

Data Independence - to have a data storage and
programming environment in which as many
types of changes in the data structure as
possible would not require changes in the
application programs that use them.
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Major DBMS Approaches

Hierarchical - navigational

Network - navigational

Relational - became commercially viable in
about 1980.

Object-oriented - useful for a variety of niche
applications.
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Hierarchical & Network

Called navigational approaches because
of the way that programs have to
“navigate” through hierarchies and
networks of data to find needed data.

Developed in the 1960s and 1970s.

Somewhat similar in structure.
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Hierarchical & Network

Suitable only for mainframe computers

were an elegant solution to the
redundancy/integration problem at the time

Complex, difficult to work

Now considered legacy systems
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Relational Database

Became commercially viable in about
1980

Soon became the preferred DBMS
approach and it has remained so ever
since.
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Object-oriented

Has proven useful for a variety of niche
applications

It is interesting to note that some of the
key object-oriented database concepts
have found their way into some of the
mainstream relational DBMSs and some
are described as taking a hybrid
object/relational approach to database.
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