Master the ABCs of Database Entities with Real-life Examples

Table of content

  1. Introduction
  2. Understanding Entities and their Types
  3. Creating Entities with Examples
  4. Understanding Relationship between Entities
  5. Normalization: How it helps in Database Design
  6. Real-Life Examples of Entity Relationship Modeling
  7. Best Practices for Entity Relationship Diagramming
  8. Conclusion


In the world of database management, entities are an essential concept that every developer needs to understand. An entity is simply an object or concept with characteristics that distinguish it from other objects or concepts. In the context of a database, entities are the building blocks of data that help organize and categorize information in a meaningful way.

In this article, we will explore the ABCs of database entities, from what they are to how they are used in real-world applications. We will cover the following topics:

  • What are entities and why are they important?
  • How entities relate to tables, rows, and columns in a database
  • Types of entities, including simple and composite entities
  • Real-life examples of entities in action, such as customer orders and employee schedules

By the end of this article, you will have a solid understanding of what entities are and how they can be used to store and manage data effectively. Whether you are a beginner in Android development or an experienced programmer, this article will provide you with a foundation of knowledge that will help you build better apps and databases. So, let's dive in and master the ABCs of database entities!

Understanding Entities and their Types

Entities are the building blocks of any database. They are the objects or concepts that we want to store data about. For example, if we were building a database for a library, the entities might include books, authors, borrowers, and loans. In Android development, is essential to building effective and efficient applications.

Here are some key concepts to understand:

1. Entity Types

In a database, entities fall into three main types:

  • Strong entities: These entities can exist independently and have their own unique identifier (or primary key). Examples in our library database might include books and authors.
  • Weak entities: These entities depend on another entity for their existence and do not have a unique identifier of their own. Examples might include loans, which depend on both books and borrowers.
  • Associative entities: These entities represent the relationships between other entities. In our library database, a good example might be an entity that represents the relationship between borrowers and the books they have checked out.

2. Entity Attributes

Entities also have attributes, which are characteristics or properties that describe the entity. For example, a book might have attributes like title, author, and publication date. Attributes can be further classified into:

  • Simple attributes: Simple attributes cannot be further subdivided. For example, a borrower's name or a book's ISBN would be simple attributes.
  • Composite attributes: Composite attributes are made up of multiple simple attributes. For example, a borrower's address might be made up of street, city, state, and zip code.
  • Derived attributes: Derived attributes are calculated from other attributes. For example, a book's age might be derived from its publication date.

3. Entity Relationships

Finally, entities can be related to one another in different ways. Some common types of relationships include:

  • One-to-one: For example, a borrower might have only one library card and a library card might belong to only one borrower.
  • One-to-many: For example, a borrower might have checked out multiple books, but each book can only be checked out by one borrower at a time.
  • Many-to-many: For example, a borrower might have borrowed multiple books, and each book might have been borrowed by multiple borrowers.

By , we can begin to design and build effective databases in our Android applications. This is a foundational concept that developers must master in order to create robust, scalable, and efficient applications.

Creating Entities with Examples

In database design, an entity is a specific object or concept that is being modeled within the database. Entities represent the various types of data that are stored in the database, such as customers, orders, products, and so on. Each entity is defined by a set of attributes, which are the specific pieces of information that are associated with that entity.

To create entities within your database, you need to identify the different types of objects or concepts that you want to store information about. For example, if you are building an e-commerce application, you might need to create entities for customers, orders, products, and payments. To create these entities, you would follow these general steps:

  • Identify the name of the entity (e.g. Customer, Order, Product, Payment).
  • Identify the attributes that are associated with each entity (e.g. customer name, order date, product name, payment amount).
  • Determine the data type of each attribute (e.g. string, date/time, number).
  • Create a table for each entity, with columns for each attribute.

Let's look at an example to see how this works in practice. Suppose that we are building a simple e-commerce application that allows customers to place orders for products. Here are the entities that we might need to create:

Customer Entity

Attribute Data Type
Customer ID integer
First Name string
Last Name string
Email Address string
Phone Number string

Product Entity

Attribute Data Type
Product ID integer
Product Name string
Description string
Price number

Order Entity

Attribute Data Type
Order ID integer
Order Date date/time
Customer ID integer
Product ID integer

Payment Entity

Attribute Data Type
Payment ID integer
Order ID integer
Payment Date date/time
Amount number

By creating these four entities, we can store all of the necessary information about customers, products, orders, and payments in our database. Once we have created the entities, we can start to build out the rest of our application, using queries and other database operations to retrieve and manipulate the data as needed.

Understanding Relationship between Entities

One of the key concepts in database design is understanding the relationship between entities, or how different pieces of data are connected to each other. This is important because it can help you design your database in a way that is efficient, easy to use, and avoids errors or inconsistencies in your data.

Here are some common types of relationships that you might encounter in a database:

  • One-to-one: In this type of relationship, each instance of one entity is associated with exactly one instance of another entity. For example, in a database of employees and their personal information, each employee might be associated with one specific social security number.
  • One-to-many: In this type of relationship, each instance of one entity can be associated with multiple instances of another entity. For example, in a database of customers and their orders, each customer might have multiple orders associated with them.
  • Many-to-many: In this type of relationship, multiple instances of one entity can be associated with multiple instances of another entity. For example, in a database of students and their courses, each student might be enrolled in multiple courses and each course might have multiple students enrolled.

It's important to understand these relationships because they can affect how you design your database and how you query your data. For example, if you have a many-to-many relationship between two entities, you might need to use a join table to associate them in your database. Or, if you have a one-to-many relationship, you might need to use a foreign key to link the entities together.

Here are some real-life examples of relationships between entities:

  • In a social media app, each user might have multiple friends (one-to-many).
  • In an e-commerce app, each order might have multiple products and each product might be associated with multiple orders (many-to-many).
  • In a library app, each book might have multiple authors and each author might have written multiple books (many-to-many).

By understanding the relationships between entities in your database, you can create a database structure that is both efficient and easy to use.

Normalization: How it helps in Database Design

Normalization is a process used in database design to organize data in a way that reduces redundancy and improves performance. In a normalized database, data is organized into separate tables based on its characteristics, minimizing duplication of information and ensuring that each piece of data is stored in only one place. This makes data retrieval more efficient and simplifies the maintenance of the database over time.

Benefits of Normalization

Normalization offers several benefits for database design, including:

  • Reduced redundancy: Data is stored in only one place, which minimizes the potential for inconsistencies and errors.
  • Improved performance: The database can process queries more quickly, since it does not have to search through redundant data.
  • Simplified maintenance: Changes to the database structure or data can be made more easily, since each piece of data is stored in only one place.

Levels of Normalization

There are several levels of normalization, each with its own set of rules and guidelines.

  • First Normal Form (1NF): This level requires that each table have a primary key, and that each column in the table only contain atomic values (i.e. indivisible and not multi-valued).
  • Second Normal Form (2NF): This level requires that all non-key attributes in a table be dependent on the primary key. This means that if a table has composite primary key – composed of more than one column – then all non-key attributes must be dependent on all columns of the composite primary key.
  • Third Normal Form (3NF): This level requires that all non-key attributes in a table be dependent on the primary key, and not on any other non-key attributes in the table. This eliminates transitive dependencies, where a non-key attribute depends on another non-key attribute.

Overall, normalization plays a critical role in database design by enhancing efficiency and helping to ensure data integrity. By following the rules and guidelines of normalization, developers can create databases that are better organized, easier to maintain, and more scalable over time.

Real-Life Examples of Entity Relationship Modeling


Entity Relationship Modeling is an essential concept in database design. It involves creating a visual representation of how different entities in a database are related to each other. Here are some :

  • Banking System: In a banking system, customer and account are two entities that are related to each other. A customer can have multiple accounts, and each account belongs to a single customer. This relationship can be represented using an entity-relationship diagram, where a customer entity is connected to multiple account entities.

  • E-commerce System: In an e-commerce system, customer, order, and product are three entities that are related to each other. A customer can place multiple orders, and each order can have multiple products. This relationship can be represented using an entity-relationship diagram, where a customer entity is connected to multiple order entities, and each order entity is connected to multiple product entities.

  • Social Media Platform: In a social media platform, user, post, and comment are three entities that are related to each other. A user can create multiple posts, and each post can have multiple comments. This relationship can be represented using an entity-relationship diagram, where a user entity is connected to multiple post entities, and each post entity is connected to multiple comment entities.

  • Healthcare System: In a healthcare system, patient, doctor, and appointment are three entities that are related to each other. A patient can have multiple appointments, and each appointment belongs to a single patient and doctor. This relationship can be represented using an entity-relationship diagram, where a patient entity is connected to multiple appointment entities, and each appointment entity is connected to a single patient and doctor entity.

Entity relationship modeling is an essential skill for database designers and developers. It helps to create a clear picture of how different entities in a database are related to each other. By using entity-relationship diagrams, designers can improve the efficiency and effectiveness of their database systems.

Best Practices for Entity Relationship Diagramming

Entity Relationship Diagrams (ERDs) are a popular tool used to visualize database entities and their relationships. ERDs can help you design and optimize your database schema more efficiently. Here are some that can help you create effective visual representations of your database entities and relationships:

1. Identify and define all entities involved
Identifying and defining all entities involved is the first step in entity relationship diagramming. You need to consider all the data that is required for your application and organize it into entities. These entities should be given unique and meaningful names, and their attributes should be clearly defined.

2. Determine the attribute types
After defining the entities and their attributes, you need to determine the attribute types. There are many attribute types such as integers, floats, dates, strings, and more. It is important to choose the right attribute types for each entity and attribute as it will define how data is stored, retrieved, and processed.

3. Establish relationships
Next, establish the relationships between the entities. You can use various notations such as lines, crow's feet, and arrows, to represent the relationships. The relationships can be one-to-one, one-to-many, or many-to-many, so make sure to choose the right notation based on the relationship type.

4. Define cardinality
Cardinality is the number of instances in one entity related to the number of instances in another entity. This is crucial to define properly, as it affects your data retrieval and processing. The cardinality can be one-to-one, one-to-many, many-to-one, or many-to-many.

5. Keep it simple
ERDs can get complex pretty quickly, so it is essential to keep them simple and easy to understand for anyone who accesses it. So, avoid including unnecessary entities and attributes in the ERDs.

Following these best practices can help you create effective entity relationship diagrams for your database entities that can improve your database schema design and optimization.



In , mastering the ABCs of database entities is essential for any Android application developer who wants to create robust and efficient apps. Understanding the different types of database entities and their relationships to one another can help developers design better data structures, improve application performance, and reduce the likelihood of errors and bugs.

By using real-life examples, we hope we have demystified database entities and made them more approachable to developers of all levels. We encourage you to continue exploring this topic and applying your knowledge to your Android development projects. Whether you are working on a small application or a complex system, a solid understanding of database entities will undoubtedly help you build better, more successful applications.

Cloud Computing and DevOps Engineering have always been my driving passions, energizing me with enthusiasm and a desire to stay at the forefront of technological innovation. I take great pleasure in innovating and devising workarounds for complex problems. Drawing on over 8 years of professional experience in the IT industry, with a focus on Cloud Computing and DevOps Engineering, I have a track record of success in designing and implementing complex infrastructure projects from diverse perspectives, and devising strategies that have significantly increased revenue. I am currently seeking a challenging position where I can leverage my competencies in a professional manner that maximizes productivity and exceeds expectations.
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