Learn about the fundamental concepts of databases, why, how, and when they're used.

Fundamentals of Web Programming

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 module, 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.

Database Fundamentals

## What is an entity?

An entity is an object in the real world with an independent existence that can be differentiated from other objects. An entity might be:

* An object with physical existence (e.g., a lecturer, a student, a car).
* An object with conceptual existence (e.g., a course, a job, a position).

Each entity has **attributes** which are the
particular properties that describe it. For example, an EMPLOYEE entity may be described by the employee’s name, age, address, salary, etc. A particular entity will have a value for each of its attributes (e.g. an employee named Steve, who is 23 years old, lives in Ohio, and earns $50,000, etc.). The attribute values that describe each entity become a major part of the data stored in the database. 

## Entity types and entity sets

A database usually contains groups of entities that are similar. For example, a company employing hundreds of employees may want to
store similar information concerning each of their employees. These EMPLOYEE entities share the same attributes (like `Name`, `Salary`, `Age`), but each entity has its own values for each attribute. An **entity type** defines a collection (or set) of entities that have the same attributes. Each entity type in the database is described by its name and attributes. 

The figure below shows the EMPLOYEE entity type as well as a list of some of the attributes for that type. A few individual entities are also illustrated, along with the values of their attributes. 

# What is an entity?

An entity is an object in the real world with an independent existence that can be differentiated from other objects. An entity might be:

* An object with physical existence (e.g., a lecturer, a student, a car).
* An object with conceptual existence (e.g., a course, a job, a position).

Each entity has **attributes** which are the
particular properties that describe it. For example, an EMPLOYEE entity may be described by the employee’s name, age, address, salary, etc. A particular entity will have a value for each of its attributes (e.g. an employee named Steve, who is 23 years old, lives in Ohio, and earns $50,000, etc.). The attribute values that describe each entity become a major part of the data stored in the database. 

# Entity types and entity sets

A database usually contains groups of entities that are similar. For example, a company employing hundreds of employees may want to
store similar information concerning each of their employees. These EMPLOYEE entities share the same attributes (like `Name`, `Salary`, `Age`), but each entity has its own values for each attribute. An **entity type** defines a collection (or set) of entities that have the same attributes. Each entity type in the database is described by its name and attributes. 

The figure below shows the EMPLOYEE entity type as well as a list of some of the attributes for that type. A few individual entities are also illustrated, along with the values of their attributes. 

In this lesson, we will discuss the first component of an ER diagram: entities.

Before We Begin

Fundamental Concepts

Data Modeling

Entity-Relationship Data Model

The Relational Data Model

Functional Depedencies

Normalization

Types of Databases

Conclusion

Entities, Entity Sets and Entity Types

What is an entity?