Today’s AgendaToday’s Agenda Any questions about the assignment (due Mon)?Any questions about the assignment (due Mon)? QuizQuiz Quiz reviewQuiz review Homework for Friday:Homework for Friday:

Watch the two videos on the Coursera db website that Watch the two videos on the Coursera db website that deal with relational algebradeal with relational algebra

And/or read up on it from your favorite resourceAnd/or read up on it from your favorite resource Formalize concepts of database anomalies Formalize concepts of database anomalies If time, finish off our Transit TablesIf time, finish off our Transit Tables

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Today’s slides from:Today’s slides from:Chapter 4Chapter 4

The Database Management The Database Management System ConceptSystem Concept

Fundamentals of Database Management Systemsby

Mark L. Gillenson, Ph.D.

University of Memphis

John Wiley & Sons, Inc.

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ObjectivesObjectives

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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The Database ConceptThe Database Concept

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 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

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

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

Insertion Anomaly Insertion Anomaly - e.g., General Hardware cannot add - 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 Update Anomaly - redundant data in the database file - redundant data in the database file must be updated each place it exists when it changesmust 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.

How would you represent How would you represent Sales and Customers?Sales and Customers?

What is the cardinality/modality of the What is the cardinality/modality of the relationshiprelationship

How should we handle it?How should we handle it?

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In order to avoid anomalies, In order to avoid anomalies, we normalize our tableswe normalize our tables

But first… we will start a side trip into Relational But first… we will start a side trip into Relational Algebra firstAlgebra first Need to know the basic rules for how relational data Need to know the basic rules for how relational data

is updated/deleted/combined/selected/projected in is updated/deleted/combined/selected/projected in order to fully understand the implications of order to fully understand the implications of normalizationnormalization

Do your homework for Friday – dive into Do your homework for Friday – dive into relational algebrarelational algebra

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