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Database Normalization and ERD Basics
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04/18/2023 1
Data Base NormalizationAnd
Entity Relationship Diagrams
04/18/2023 2
Normalization
• Database normalization is the process of removing redundant data from your tables in to improve storage efficiency, data integrity, and scalability.
• Normalization generally involves splitting existing tables into multiple ones, which must be re-joined or linked each time a query is issued.
• Edgar F. Codd originally established three normal forms: 1NF, 2NF and 3NF. There are now others that are generally accepted, but 3NF is widely considered to be sufficient for most applications. Most tables when reaching 3NF are also in BCNF (Boyce-Codd Normal Form).
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1st Normal Form
Rules of First Normal Form1. Create separate tables for each group of
related data and ensure each row is unique by identifying a primary key .
2. Eliminate duplicate columns from the same table.
**Primary key : A primary key is either a single field or combined set of fields that
uniquely identify a single row of data in a table
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1st Normal Form Example
• Let say we want to build a database that can manage Books.
• We can create an entity(table) like thisEntity Book
Fields
Title
Author1
Author2
ISBN
Subject
Pages
Publisher
Title Author1 Author2 ISBN SubjectPages
Publisher
Database System Concepts
Abraham Silberschatz
Henry F. Korth
72958863
MySQL, Computers
1168
McGraw-Hill
Operating System Concepts
Abraham Silberschatz
Henry F. Korth
471694665 Computers 944
McGraw-Hill
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1st Normal Form
• In our Table 1, we have two violations of First Normal Form:
• First, we have more than one author field, • Second, our subject field contains more than
one piece of information. With more than one value in a single field, it would be very difficult to search for all books on a given subject.
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1st Normal FormBefore Normalization
Title Author1 Author2 ISBN Subject Pages PublisherDatabase System
ConceptsAbraham
SilberschatzHenry F.
Korth 72958863MySQL,
Computers 1168McGraw-
HillOperating System
ConceptsAbraham
SilberschatzHenry F.
Korth47169466
5 Computers 944McGraw-
Hill
1st Normal FormTitle Author ISBN Subject Pages Publisher
Database System Concepts
Abraham Silberschatz 72958863 MySQL 1168
McGraw-Hill
Database System Concepts Henry F. Korth 72958863
Computers 1168
McGraw-Hill
Operating System Concepts Henry F. Korth 471694665
Computers 944
McGraw-Hill
Operating System Concepts
Abraham Silberschatz 471694665
Computers 944
McGraw-Hill
We now have two rows for a single book. Additionally, we would be violating the Second Normal Form.A better solution to our problem would be to separate the data into separate tables- an Author table and a Subject table to store our information, removing that information from the Book table:
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1st Normal Form
1stNormal Form
Subjects Table Authors TableSubject_ID Subject Author_ID Last Name First Name
1 MySQL 1 Silberschatz Abraham2 Computers 2 Korth Henry
Books Table
ISBN TitlePage
s Publisher
72958863Database System
Concepts 1168McGraw-
Hill
471694665Operating System
Concepts 944McGraw-
Hill
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2nd Normal Form
• Meet all the requirements of 1st Normal Form.• Remove redundant data and place them in
separate tables• Create relationships between tables through
the use of foreign keys.
Foreign Key : The foreign key create the foundation of a relationship between two tables by inserting the primary key from one table into another table
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2nd Normal FormPublisher Table
Publisher_ID Publisher Name1 McGraw-Hill
Books TableISBN Title Pages Publisher_ID
72958863 Database System Concepts 1168 1471694665 Operating System Concepts 944 1
Here we have a one-to-many relationship between the book table and the publisher. A book has only one publisher, and a publisher will publish many books. When we have a one-to-many relationship, we place a foreign key in the Book Table, pointing to the primary key of the Publisher Table.
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3rd Normal Form
• Meet all the requirements of 2nd Normal Form• Remove all attributes from a table that are not
directly dependant on primary key .
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Entity Relationship Diagrams
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Entity and Attribute
• An entity is a business object that represents a group, or category of data.
• An attribute is a sub-group of information within an entity.
• Entity Table• Attribute Column
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Entity Relationship Models
• Mandatory Relationships• Optional Relationships• Many-to-Many Relationships• One-to-Many Relationships• One-to-One Relationships• Recursive Relationships
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Mandatory, Many-to-Many
INSTRUCTOR STUDENT
INSTRUCTOR STUDENT
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Optional, Many-to-Many
DEPARTMENT STUDENT
DEPARTMENT STUDENT
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Optional/Mandatory,Many-to-Many
INSTRUCTOR SKILL
INSTRUCTOR SKILL
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Optional/Mandatory,One-to-Many
PRODUCT VENDOR
PRODUCT VENDOR
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Mandatory, One-to-One
AUTOMOBILE ENGINE
AUTOMOBILE ENGINE
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Recursive
EMPLOYEEsupervises
is supervised by
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Resolving Many-to-Many Relationships
• Many-to-many relationships should be avoided. We can resolve a many-to-many relationship by dividing it into two one-to-many relationships.
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Resolving Many-to-Many Relationships
SALES ORDERS INV. ITEMS
SALES ORDERS INV. ITEMSORDER ITEMS
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Example (ER Diagram)
SALES ORDERS
INV. ITEMSORDER ITEMS
CLERKSCUSTOMERS
HR Schema ER Diagram
