1. Chapter 4
Relational Databases

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Learning Objectives
Explain the importance and advantages of databases
Describe the difference between database systems and file-based legacy systems.
Explain the difference between logical and physical views of a database.
Explain fundamental concepts of database systems such as DBMS, schemas, the data dictionary, and DBMS languages.
Describe what a relational database is and how it organizes data.
Create a set of well-structured tables to store data in a relational database.
Perform simple queries using the Microsoft Access database.

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Data Hierarchy
Field
Attributes about an entity
Record
Related group of fields
File
Related group of records
Database
Related group of files

4. Data Redundancy / Independence
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Data Redundancy / Independence
File Approach
Database Approach
A, B, C, D
Sales
A, B, C, D, E, F, G
A, C, E, F
Shipping
Database
Management
System
A, D, E, G
Billing
Sales
Shipping
Billing

5. Advantages of Database Systems
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Advantages of Database Systems
Data Integration
Files are logically combined and made accessible to various systems.
Data Sharing
With data in one place it is more easily accessed by authorized users.
Minimizing Data Redundancy & Data Inconsistency
Eliminates Reduces the same data being stored in multiple files, thus reducing inconsistency in multiple versions of the same data.
Data Independence
Data is separate from the programs that access it. Changes can be made to the data without necessitating a change in the programs and vice versa.
Cross-Functional Analysis
Relationships between data from various organizational departments can be more easily combined.

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Database Terminology
Database Management System (DBMS)
Interface between software applications and the data in files.
Database Administrator (DBA)
Person responsible for maintaining the database
Data Dictionary
Information about the structure of the database
Field names, descriptions, uses

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Logical Vs. Physical
Physical View
Depends on explicitly knowing:
How is the data actually arranged in a file
Where is the data stored on the computer
Logical View
Conceptual Organization of Data
Separates storage of data from use of the data
Unnecessary to explicitly know how and where data is stored.

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Schemas
Describe the logical structure of a database
Conceptual Level
Organization wide view of the data
External Level
Individual Users view of the data
Each view is a subschema
Internal Level
Describes how data are stored and accessed
Description of: Records, Definitions, Addresses & Indexes

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DBMS Languages
Data Definition Language (DDL)
Builds the data dictionary
Creates the database
Describes the subschema
Specifies record and/or field security constraints
Data Manipulation Language (DML)
Changes the content in the database
Updates, Insertions and Deletions
Data Query Language (DQL)
Enable the retrieval, sorting, & display of data from the database

10. Types of Database Structures
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Types of Database Structures
Hierarchical
Data is organized in a tree like structure
Each Child has only 1 parent, but each parent can have many children
Network
allows each record to have multiple parent and child records
Object-Oriented
information is represented in the form of objects
database and applications are not independent
Associated …
Relational

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Relational Database
Relational Data model represents the conceptual and external level schemas as if data are stored in tables
Table
Each Row, a Tuple, contains data about one instance of an entity
This is equivalent to a Record
Each Column, contains data about one attribute of an entity
This is equivalent to a Field

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A Relational Table
Row (Record)
Column (Field)
Each row contains multiple attributes describing an instance of the entity. In this case inventory.
Same type of data

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Attributes
Primary Key
An attribute or combination of attributes that can be used to Uniquely identify a specific row(record) in a table.
Foreign Key
An attribute in one table that is a Primary key in another table.
Used to link the two tables.

14. Each row is called a tuple, which rhymes with “couple.”

15. Each row contains data about a specific occurrence of the type of entity in the table.

16. Each column in a table contains information about a specific attribute of the entity.

17. A primary key is the attribute or combination of attributes that uniquely identifies a specific row in a table.

18. In some tables, two or more attributes may be joined to form the primary key.

19. STUDENTS
Student ID
Last Name
First Name
Phone No.
Advisor No.
Simpson
Alice
1418
Sanders
Ned
Moore
Artie
1503
ADVISORS
Advisor No.
Last Name
First Name
Office No.
1418
Howard
Glen
420
1419
Melton
Amy
316
1503
Zhang Xi
202
1506
Radowski
J.D.
203
A foreign key is an attribute in one table that is a primary key in another table.

20. Foreign keys are used to link tables together.
STUDENTS
Student ID
Last Name
First Name
Phone No.
Advisor No.
Simpson
Alice
1418
Sanders
Ned
Moore
Artie
1503
ADVISORS
Advisor No.
Last Name
First Name
Office No.
1418
Howard
Glen
420
1419
Melton
Amy
316
1503
Zhang Xi
202
1506
Radowski
J.D.
203
Foreign keys are used to link tables together.

21. STUDENTS
Student ID
Last Name
First Name
Phone No.
Advisor No.
Simpson
Alice
1418
Sanders
Ned
Moore
Artie
1503
ADVISORS
Advisor No.
Last Name
First Name
Office No.
1418
Howard
Glen
420
1419
Melton
Amy
316
1503
Zhang Xi
202
1506
Radowski
J.D.
203
Other non-key attributes in each table store important information about the entity.

22. Database Design Errors
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Database Design Errors
If the database is not designed properly data errors can occur:
Update Anomaly
Changes to existing data are not correctly recorded
Due to multiple records with the same data attributes
Insert Anomaly
Unable to add a record to the database
Delete Anomaly
Removing a record also removes unintended data from the database

23. In the above, simplified example, a number of problems arise.
Student ID
Last Name
First Name
Phone No.
Course No.
Section
Day
Time
Simpson
Alice
ACCT-3603 1 M
9:00 AM
FIN-3213 3 Th
11:00 AM
MGMT-3021 11
12:00 PM
Sanders
Ned
ACCT-3433 2 T
10:00 AM 5 W
8:00 AM
ANSI-1422 7 F
Moore
Artie
In the above, simplified example, a number of problems arise.

24. This problem is referred to as an update anomaly.
Student ID
Last Name
First Name
Phone No.
Course No.
Section
Day
Time
Simpson
Alice
ACCT-3603 1 M
9:00 AM
FIN-3213 3 Th
11:00 AM
MGMT-3021 11
12:00 PM
Sanders
Ned
ACCT-3433 2 T
10:00 AM 5 W
8:00 AM
ANSI-1422 7 F
Moore
Artie
Suppose Alice Simpson changes her phone number. You need to make the change in three places. If you fail to change it in all three places or change it incorrectly in one place, then the records for Alice will be inconsistent.
This problem is referred to as an update anomaly.

25. This problem is referred to as an insert anomaly.
Student ID
Last Name
First Name
Phone No.
Course No.
Section
Day
Time
Simpson
Alice
ACCT-3603 1 M
9:00 AM
FIN-3213 3 Th
11:00 AM
MGMT-3021 11
12:00 PM
Sanders
Ned
ACCT-3433 2 T
10:00 AM 5 W
8:00 AM
ANSI-1422 7 F
Moore
Artie
What happens if you have a new student to add, but he hasn’t signed up for any courses yet?
Or what if there is a new class to add, but there are no students enrolled in it yet? In either case, the record will be partially blank.
This problem is referred to as an insert anomaly.

26. This problem is referred to as a delete anomaly.
Student ID
Last Name
First Name
Phone No.
Course No.
Section
Day
Time
Simpson
Alice
ACCT-3603 1 M
9:00 AM
FIN-3213 3 Th
11:00 AM
MGMT-3021 11
12:00 PM
Sanders
Ned
ACCT-3433 2 T
10:00 AM 5 W
8:00 AM
ANSI-1422 7 F
Moore
Artie
If Ned withdraws from all his classes and you eliminate all three of his rows from the table, then you will no longer have a record of Ned. If Ned is planning to take classes next semester, then you probably didn’t really want to delete all records of him.
This problem is referred to as a delete anomaly.

27. This approach is also fraught with problems:
Student ID
Last Name
First Name
Phone No.
Class 1
Class 2
Class 3
Class 4
Simpson
Alice
ACCT-3603
FIN-3213
MGMT-3021
Sanders
Ned
ACCT-3433
ANSI-1422
Moore
Artie
This approach is also fraught with problems:
How many classes should you allow in building the table?
The above table is quite simplified. In reality, you might need to allow for 20 or more classes (assuming a student could take many 1-hour classes). Also, more information than just the course number would be stored for each class. There would be a great deal of wasted space for all the students taking fewer than the maximum possible number of classes.
Also, if you wanted a list of every student taking MGMT-3021, notice that you would have to search multiple attributes.

28. The solution to the preceding problems is to use a set of tables in a relational database.
Each entity is stored in a separate table, and separate tables or foreign keys can be used to link the entities together.

29. Note that within each table, there are no duplicate primary keys and no null primary keys.
Consistent with the entity integrity rule.

30. STUDENTS
Student ID
Last Name
First Name
Phone No.
Advisor No.
Simpson
Alice
1418
Sanders
Ned
Moore
Artie
1503
ADVISORS
Advisor No.
Last Name
First Name
Office No.
1418
Howard
Glen
420
1419
Melton
Amy
316
1503
Zhang Xi
202
1506
Radowski
J.D.
203
Advisor No. is a foreign key in the STUDENTS table. Every incident of Advisor No. in the STUDENTS table either matches an instance of the primary key in the ADVISORS table or is null.

31. Add a student here.
Leaves no blank spaces.
Add a course here.
Leaves no blank spaces.
When a particular student enrolls for a particular course, add that info here.

32. Ned still exists in the student table.
Even if Ned was the only student in the class, ACCT-3603 still exists in the course table.
If Ned Sanders drops ACCT-3603, remove Ned’s class from this table.

33. Design Requirements for Relational Database
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Design Requirements for Relational Database
Every column must be single valued.
Primary keys must contain data (Not Null).
Entity Integrity
Foreign Keys must contain the same data as the primary key in another table.
Referential Integrity
All other attributes must identify a characteristic of the table identified by the primary key.

34. Normalizing Relational Databases
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Normalizing Relational Databases
Initially one table is used for all the data in a database
Following rules, the table is decomposed into multiple tables related by:
Primary Key – Foreign key integration
Decomposed set of tables are in third normal form (3NF)
First Normal Form:
A relation is in first normal form if the domain of each attribute contains only atomic values, and the value of each attribute contains only a single value from that domain.
Second Normal Form:
No non-prime attribute in the table is functionally dependent on a proper subset of any candidate key
Third Normal Form:
Every non-prime attribute is non-transitively dependent on every candidate key in the table. The attributes that do not contribute to the description of the primary key are removed from the table. In other words, no transitive dependency is allowed.

35. Semantic Data Modeling
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Semantic Data Modeling
Using Knowledge of Business Processes
Diagram is created of the Database System
Entity-Relationship Diagram or E-R Diagram
In accounting we use a special form:
Resource, Event, Agent or REA diagram
Diagram becomes Blue-print of Database structure
Database designed this way must still follow rules of a Normalized Database to eliminate design errors

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Creating Queries

37. Microsoft Access Query#1
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Microsoft Access Query#1

38. Microsoft Access Query#2
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Microsoft Access Query#2

39. Microsoft Access Query#3
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Microsoft Access Query#3

40. Microsoft Access Query#4
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Microsoft Access Query#4

41. Microsoft Access Query#5
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Microsoft Access Query#5