Gain insights into fundamental database concepts, relational databases, and entity-relationship diagrams. Learn about normalization techniques and basics of SQL to enhance database efficiency.

Databases are universal - they underlie the technology you use every day. They're a crucial component of everything from telecommunications systems, banking systems, and video games to just about any other software system that maintains some amount of persistent data.

In this course, you'll learn about the fundamental concepts of databases, why and when they're used, what relational databases are, and entity-relationship diagrams. You will also be exposed to techniques like normalization that help to increase the efficiency of databases. You'll wrap up with a look at the basics of Structured Query Language (SQL). 

After completing this course, you will be able to move onto more advanced courses involving database systems and SQL.

Database Design Fundamentals for Software Engineers

## Weak entity types

Entity types that do not have key attributes of their own are called weak entity types like the DEPENDENT entity type in the [company database](https://www.educative.io/courses/database-design-fundamentals/intro-to-entity-relationship-model). 

In contrast, regular entity types that do have a key attribute are called **strong entity types**. Entities belonging to a weak entity type are identified by being related to specific entities from another entity type in combination with one of their attribute values. We call this other entity type the **identifying or owner entity type**, and we call the relationship type that relates a weak entity type to its owner the **identifying relationship** of the weak entity type. 


Consider the entity type DEPENDENT, related to EMPLOYEE, which is used to keep track of the dependents of each employee via a 1:N relationship. In the diagram below, the attributes of DEPENDENT are `Name`, `Birth_Date`, and `Relationship` (to the employee). Two dependents of two distinct employees may, by chance, have the same values for `Name`, `Birth_Date`, and
`Relationship`, but they are still distinct entities. They are identified as distinct entities only after determining the particular EMPLOYEE entity to which each dependent is
related. 



In ER diagrams, both a weak entity type and its identifying relationship are distinguished by surrounding their boxes and diamonds with double lines. 

# Weak entity types

Entity types that do not have key attributes of their own are called weak entity types like the DEPENDENT entity type in the [company database](https://www.educative.io/courses/database-design-fundamentals/intro-to-entity-relationship-model). 

In contrast, regular entity types that do have a key attribute are called **strong entity types**. Entities belonging to a weak entity type are identified by being related to specific entities from another entity type in combination with one of their attribute values. We call this other entity type the **identifying or owner entity type**, and we call the relationship type that relates a weak entity type to its owner the **identifying relationship** of the weak entity type. 


Consider the entity type DEPENDENT, related to EMPLOYEE, which is used to keep track of the dependents of each employee via a 1:N relationship. In the diagram below, the attributes of DEPENDENT are `Name`, `Birth_Date`, and `Relationship` (to the employee). Two dependents of two distinct employees may, by chance, have the same values for `Name`, `Birth_Date`, and
`Relationship`, but they are still distinct entities. They are identified as distinct entities only after determining the particular EMPLOYEE entity to which each dependent is
related. 



In ER diagrams, both a weak entity type and its identifying relationship are distinguished by surrounding their boxes and diamonds with double lines. 

In this lesson, we will look at the last component of our ER model.

Introduction

Fundamental Concepts

Data Modeling

Entity-Relationship Data Model

The Relational Data Model

Functional Dependencies

Normalization

Structured Query Language

Conclusion

Weak Entity Types

Weak entity types