chapter 3 the database management system concept fundamentals of database management systems, 2 nd...

Chapter 3Chapter 3The Database Management The Database Management

System ConceptSystem Concept

Fundamentals of Database Management Systems, 2nd ed

by

Mark L. Gillenson, Ph.D.

University of Memphis

John Wiley & Sons, Inc.

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Chapter ObjectivesChapter Objectives

Discuss the problems encountered in a Discuss the problems encountered in a nondatabase information systems nondatabase information systems environment.environment.

Discuss the nature of data.Discuss the nature of data.

Define data-related terms such as entity Define data-related terms such as entity and attribute.and attribute.

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Define storage-related terms such as field, Define storage-related terms such as field, record, and file.record, and file.

Identify the four basic operations Identify the four basic operations performed on stored data.performed on stored data.

Compare sequential access of data with Compare sequential access of data with direct access of data.direct access of data.

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List the five basic principles of the List the five basic principles of the database concept. database concept.

Describe how data can be considered to Describe how data can be considered to be a manageable resource. be a manageable resource.

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List the three problems created by data List the three problems created by data redundancy. redundancy.

Describe the nature of data redundancy Describe the nature of data redundancy among many files. among many files.

Explain the relationship between data Explain the relationship between data integration and data redundancy in one integration and data redundancy in one file.file.

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State the primary defining feature of a State the primary defining feature of a database management system. database management system.

Explain why the ability to store multiple Explain why the ability to store multiple relationships is an important feature of the relationships is an important feature of the database approach.database approach.

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Explain why providing support for such Explain why providing support for such control issues as data security, backup control issues as data security, backup and recovery, and concurrency is an and recovery, and concurrency is an important feature of the database important feature of the database approach. approach.

Explain why providing support for data Explain why providing support for data independence is an important feature of independence is an important feature of the database approach. the database approach.

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Data Processing SystemsData Processing Systems

Data was stored in different formats in different Data was stored in different formats in different files.files.

Data was often not shared among different Data was often not shared among different programs that needed it, necessitating the programs that needed it, necessitating the duplication of data in redundant files.duplication of data in redundant files.

Little was understood about file design, resulting Little was understood about file design, resulting in redundant data within individual files.in redundant data within individual files.

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Files often could not be rebuilt after being Files often could not be rebuilt after being damaged by a software error or a damaged by a software error or a hardware failure.hardware failure.

Data was not secure and was vulnerable Data was not secure and was vulnerable to theft or malicious mischief by people to theft or malicious mischief by people inside or outside of the company.inside or outside of the company.

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Programs were usually written in such a Programs were usually written in such a manner that if the way that the data was manner that if the way that the data was stored changed, the program had to be stored changed, the program had to be modified to continue working.modified to continue working.

Changes in everything from access Changes in everything from access methods to tax tables required methods to tax tables required programming changes.programming changes.

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Data Before Database ManagementData Before Database ManagementRecords and FilesRecords and Files

Entity - a “thing” or “object” in our environment Entity - a “thing” or “object” in our environment that we want to keep track of.that we want to keep track of.

Entity set - A collection of entities of the same Entity set - A collection of entities of the same type (e.g., all of the company’s employees).type (e.g., all of the company’s employees).

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Records and FilesRecords and Files

Attribute - a property of, a characteristic of, or a Attribute - a property of, a characteristic of, or a fact that we know about an entity.fact that we know about an entity.

Some attributes have unique values within an Some attributes have unique values within an entity set.entity set.

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Record - each row of a structure like aboveRecord - each row of a structure like above

Fields - the columns, representing the factsFields - the columns, representing the facts

File - the entire structureFile - the entire structure

keyfield

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Record type - Record type - a structural description of each and a structural description of each and every record in the fileevery record in the file

Record occurrence / Record instance - a specific Record occurrence / Record instance - a specific record of the salesperson filerecord of the salesperson file

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Retrieving and Manipulating Retrieving and Manipulating DataData

Four fundamental operations can be performed on Four fundamental operations can be performed on stored data:stored data:

Retrieve or Read - looking at a record’s contents without Retrieve or Read - looking at a record’s contents without changing itchanging it

Insert - adding a new record to the file, as when a new Insert - adding a new record to the file, as when a new salesperson is hiredsalesperson is hired

Delete - deleting a record from the file, as when a salesperson Delete - deleting a record from the file, as when a salesperson leaves the companyleaves the company

Update - changing one or more of a record’s field valuesUpdate - changing one or more of a record’s field values

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Data Retrieval MethodData Retrieval Method

Sequential access - the retrieval of all or a Sequential access - the retrieval of all or a portion of the records of a file one after another, portion of the records of a file one after another, in some sequence, starting from the beginning, in some sequence, starting from the beginning, until all of the required records have been until all of the required records have been retrieved.retrieved. Physical sequential access - records are retrieved, Physical sequential access - records are retrieved,

one after the other, just as they are stored on the disk one after the other, just as they are stored on the disk device.device.

Logical sequential access - records are retrieved in an Logical sequential access - records are retrieved in an order based on the values of one or a combination of order based on the values of one or a combination of the fields.the fields.

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Data Retrieval MethodData Retrieval Method

Direct Access - the retrieval of a single record of Direct Access - the retrieval of a single record of a file or a subset of the records of a file based a file or a subset of the records of a file based on one or more values of a field or a on one or more values of a field or a combination of fields in the file.combination of fields in the file. a crucial concept in information systems todaya crucial concept in information systems today

requires hardware storage device that will requires hardware storage device that will accommodate direct accessaccommodate direct access

requires software that will take advantage of the requires software that will take advantage of the hardware’s capabilities and store and retrieve the hardware’s capabilities and store and retrieve the data in such a way that it accomplishes direct access.data in such a way that it accomplishes direct access.

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The Database ConceptThe Database Concept

1. Data as a Manageable Resource1. Data as a Manageable Resource

2. Data Integration and Data Redundancy2. Data Integration and Data Redundancy

3. Multiple Relationships3. Multiple Relationships

4. Data Control Issues4. Data Control Issues

5. Data Independence5. Data Independence

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Data as a Manageable Resource - The Data as a Manageable Resource - The creation of a data-centric environment in creation of a data-centric environment in which a company’s data can truly be which a company’s data can truly be thought of as a significant corporate thought of as a significant corporate resource. A key feature of this resource. A key feature of this environment is the ability to share data environment is the ability to share data among those inside and outside of the among those inside and outside of the company who require access to it. company who require access to it.

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Data Integration and Data Redundancy - The Data Integration and Data Redundancy - The ability to achieve data integration while at the ability to achieve data integration while at the same time storing data in a nonredundant same time storing data in a nonredundant fashion. This, alone, is the central, defining fashion. This, alone, is the central, defining feature of the database approach.feature of the database approach.

Multiple RelationshipsMultiple Relationships - The ability to store data - The ability to store data representing entities involved in multiple representing entities involved in multiple relationships without introducing data relationships without introducing data redundancy or other structural problems. redundancy or other structural problems.

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Data Control Issues - Data Control Issues - The establishment of The establishment of an environment that manages certain data an environment that manages certain data control issues, such as data security, control issues, such as data security, backup and recovery, and concurrency backup and recovery, and concurrency control.control.

Data IndependenceData Independence - The establishment of - The establishment of an environment that permits a high degree an environment that permits a high degree of data independence.of data independence.

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Data as a Manageable Data as a Manageable ResourceResource

Information systems environment:Information systems environment: HardwareHardware NetworksNetworks Applications softwareApplications software Systems softwareSystems software PeoplePeople DataData

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Historically, data has not been the highest Historically, data has not been the highest priority concern.priority concern.

As the operational, tactical, and strategic As the operational, tactical, and strategic corporate levels became more dependent corporate levels became more dependent on information systems, data increasingly on information systems, data increasingly became recognized as an important became recognized as an important corporate resource.corporate resource.

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The corporate community became The corporate community became increasingly convinced that a firm’s data increasingly convinced that a firm’s data could provide a significant competitive could provide a significant competitive advantage to the firm.advantage to the firm.

It became clear that data would have to be It became clear that data would have to be managed in an organized way.managed in an organized way.

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Needed a Needed a software utilitysoftware utility that could that could manage and protect data.manage and protect data.

Data could be a critical Data could be a critical corporate corporate resourceresource..

Out of this need was born the database Out of this need was born the database management system.management system.

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Reengineering - data is aggressively used Reengineering - data is aggressively used to redesign business processes.to redesign business processes.

Electronic commerce - a database at the Electronic commerce - a database at the heart of every web site; allows companies heart of every web site; allows companies and customers to conduct business.and customers to conduct business.

ERP systems - collections of application ERP systems - collections of application programs build around a central database.programs build around a central database.

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Data Integration and Data Data Integration and Data RedundancyRedundancy

Data integration - the ability to tie together Data integration - the ability to tie together pieces of related data within an pieces of related data within an information system.information system.

Data redundancy - the same fact about the Data redundancy - the same fact about the business environment is stored more than business environment is stored more than once within an information system.once within an information system.

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Data Redundancy - ProblemsData Redundancy - Problems

Redundant data takes up a great deal of Redundant data takes up a great deal of extra disk space. extra disk space.

If the redundant data has to be updated, it If the redundant data has to be updated, it takes additional time to do so. This can be takes additional time to do so. This can be a major performance issue.a major performance issue.

There is the potential for data integrity There is the potential for data integrity problems.problems.

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Data IntegrityData Integrity

Refers to the accuracy of the data.Refers to the accuracy of the data.

Inaccurate data leaves the whole Inaccurate data leaves the whole information system of limited value.information system of limited value.

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Data Redundancy,Data Redundancy,Data IntegrityData Integrity

When all copies of redundant data are not When all copies of redundant data are not updated consistently, a data integrity problem updated consistently, a data integrity problem exists.exists.

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Three Files with Redundant Three Files with Redundant DataData

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Three Files with a Data Three Files with a Data Integrity ProblemIntegrity Problem

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General General Hardware Hardware Company Company FilesFiles

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General Hardware Company General Hardware Company Combined FileCombined File

CustomerNumber

CustomerName

SalespersonNumber

HQ City SalespersonNumber

SalespersonName

Commission%

Yearof Hire

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AnomaliesAnomalies

Typically occur in poorly structured files.Typically occur in poorly structured files.

Problems arise when two different kinds of Problems arise when two different kinds of data, like salesperson and customer data data, like salesperson and customer data are merged into one file.are merged into one file.

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AnomaliesAnomalies Deletion Anomaly - e.g, if you delete a customer and that Deletion Anomaly - e.g, if you delete a customer and that

record was the only one for a salesperson, the record was the only one for a salesperson, the salesperson’s data is gone.salesperson’s data is gone.

Insertion Anomaly - e.g., General Hardware cannot add Insertion Anomaly - e.g., General Hardware cannot add data about a new salesperson the company just hired data about a new salesperson the company just hired until she is assigned at least one customer.until she is assigned at least one customer.

Update Anomaly - redundant data in the database file Update Anomaly - redundant data in the database file must be updated each place it exists when it changes.must be updated each place it exists when it changes.

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Database Management Database Management SystemSystem

A software utility for storing and retrieving A software utility for storing and retrieving data that gives the end-user the data that gives the end-user the impression that the data is well integrated impression that the data is well integrated even though the data can be stored with even though the data can be stored with no redundancy at all.no redundancy at all.

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Multiple Relationships - Multiple Relationships - Horizontal SolutionHorizontal Solution

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Multiple Relationships - Multiple Relationships - Vertical SolutionVertical Solution

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Data Control IssuesData Control Issues

Data securityData security

Backup and RecoveryBackup and Recovery

Concurrency ControlConcurrency Control

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Computer SecurityComputer Security

A very broad topicA very broad topic Protecting the physical hardware Protecting the physical hardware

environmentenvironment Defending against hacker attacksDefending against hacker attacks Encrypting data transmitted over networksEncrypting data transmitted over networks Educating employees on the importance of Educating employees on the importance of

protecting the company’s dataprotecting the company’s data … … and many moreand many more

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Backup and RecoveryBackup and Recovery

Data can be lost or corrupted in any of a Data can be lost or corrupted in any of a variety of ways:variety of ways: a disaster such as a fire, a hurricane, or an a disaster such as a fire, a hurricane, or an

earthquakeearthquake hackershackers computer virusescomputer viruses poorly written application programspoorly written application programs unintentional errorunintentional error

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Concurrency ProblemConcurrency Problem

Updates to a database can interfere with Updates to a database can interfere with each other in such a way that the resulting each other in such a way that the resulting data values will be incorrect.data values will be incorrect.

A database management system must be A database management system must be designed to protect its databases from designed to protect its databases from such an eventuality.such an eventuality.

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Data IndependenceData Independence

Data Dependence - if for any reason the storage Data Dependence - if for any reason the storage characteristics of the data had to be changed, characteristics of the data had to be changed, the application program itself had to be modified, the application program itself had to be modified, often extensively.often extensively.

Data Independence - to have a data storage and Data Independence - to have a data storage and programming environment in which as many programming environment in which as many types of changes in the data structure as types of changes in the data structure as possible would not require changes in the possible would not require changes in the application programs that use them.application programs that use them.

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Major DBMS ApproachesMajor DBMS Approaches

Hierarchical - navigationalHierarchical - navigational

Network - navigationalNetwork - navigational

Relational - became commercially viable in Relational - became commercially viable in about 1980.about 1980.

Object-oriented - useful for a variety of niche Object-oriented - useful for a variety of niche applications.applications.

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Hierarchical & NetworkHierarchical & Network

Called navigational approaches because Called navigational approaches because of the way that programs have to of the way that programs have to “navigate” through hierarchies and “navigate” through hierarchies and networks of data to find needed data.networks of data to find needed data.

Developed in the 1960s and 1970s.Developed in the 1960s and 1970s.

Somewhat similar in structure.Somewhat similar in structure.

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Hierarchical & NetworkHierarchical & Network

Suitable only for mainframe computersSuitable only for mainframe computers

were an elegant solution to the were an elegant solution to the redundancy/integration problem at the timeredundancy/integration problem at the time

Complex, difficult to workComplex, difficult to work

Now considered legacy systemsNow considered legacy systems

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Relational DatabaseRelational Database

Became commercially viable in about Became commercially viable in about 19801980

Soon became the preferred DBMS Soon became the preferred DBMS approach and it has remained so ever approach and it has remained so ever since.since.

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Object-orientedObject-oriented

Has proven useful for a variety of niche Has proven useful for a variety of niche applications applications

It is interesting to note that some of the It is interesting to note that some of the key object-oriented database concepts key object-oriented database concepts have found their way into some of the have found their way into some of the mainstream relational DBMSs and some mainstream relational DBMSs and some are described as taking a hybrid are described as taking a hybrid object/relational approach to database.object/relational approach to database.

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chapter 3 the database management system concept fundamentals of database management systems, 2 nd...

Documents

data processing systems

stored data

redundant data

data security

data integration

data independence

duplication of data

data processing systems