Relational Database Design and Modeling for Software Engineers
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Introduction
Course Overview
Before the Advent of Database
Fundamental Concepts
What is a Database?
Database management systems (DBMS)
Overview of Relational Databases
Relational Vs. Non-Relational Databases
Data Modeling
Introduction to Data Modeling
Levels of Data Modeling
Data Modeling Process
Best Practices in Data Modeling
Quiz
Entity-Relationship (ER) Data Modeling
Introduction to ER Models
Entities, Attributes, and Relationships
Cardinality and Participation
Attributes of Relationship Types
Weak Entity Types
Creating an ER Diagram for Employee Management System
Quiz
Introduction to the Relational Model
Relations, Tuples, and Attributes
Keys in Relational Databases
Relational Integrity Constraints
Converting ER Diagrams to Relational Model
Best Practices for ER Diagrams to Relational Models
Quiz
Introduction to Functional Dependency
Types of Functional Dependencies
Inference Rules for Functional Dependencies
Closure of Attribute Sets
Quiz
Introduction to Normalization
First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
Boyce-Codd Normal Form (BCNF)
Higher Normal Forms (4NF, 5NF)
Exercise 1
Solution to Exercise 1
Exercise 2
Solution to Exercise 2
Designing a Hospital Management System
Designing a Hotel Management System
Designing a Bank Management System
Designing an Instagram
Designing an E-commerce Platform
Designing an Online Food Delivery System
Weak Entity Types

A weak entity is an entity that cannot be uniquely identified by its own attributes alone. Unlike regular entities, weak entities depend on a strong (or owner) entity for their identification. They do not have a primary key of their own and rely on a combination of their attributes and the primary key of the owner entity to form a unique identifier.

Characteristics of Weak Entities

  • Dependent on Strong Entity: A weak entity is associated with a strong entity and relies on it for identification.
  • Partial Key: Weak entities have a partial key (also known as a discriminator), an attribute or set of attributes that can uniquely identify the weak entity within the context of the owner entity.
  • Existence Dependency: Weak entities have an existence dependency, meaning they cannot exist independently without their associated strong entity.
  • Double Rectangle Representation: In ER diagrams, weak entities are represented by double rectangles, and their relationships with strong entities are shown with double diamonds.

Example of a Weak Entity

Consider a university database with two entities: Course (strong entity) and Course Section (weak entity).

  • Strong Entity: Course
    • Attributes: Course ID, Course Name
  • Weak Entity: Course Section
    • Attributes: Section Number (partial key), Instructor, Time
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In this example:

  • Course Section cannot exist without a Course. For example, "Section 1" alone does not uniquely identify the section without knowing which Course it belongs to (e.g., "Math 101, Section 1").
  • The Course ID from Course and Section Number together uniquely identify each Course Section.
Attributes of Relationship Types
Creating an ER Diagram for Employee Management System
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Characteristics of Weak Entities

Example of a Weak Entity