What is the 3-Tier Architecture?
The 3-Tier Architecture, also known as the three-layer architecture, is a client-server software architecture that separates an application into three distinct layers, or tiers. The purpose of this architecture is to improve modularity, maintainability, scalability, reliability and flexibility of the software system.
The three tiers are:
- Client-tier: This tier represents the user interface of the application and is responsible for presenting data to the user and receiving user input. It includes the graphical user interface (GUI) components, such as web pages, forms, and widgets.
- Server-tier: This tier contains the business logic of the application and performs the core processing of the data. It is responsible for processing user requests, retrieving and manipulating data, and performing complex operations. It includes modules such as controllers, services, and APIs.
- Data Tier: This tier is responsible for managing the data storage and retrieval in the system. It includes the database or file system where data is stored, as well as the data access layer (DAL) that interacts with the database to read and write data.
The three tiers are connected through well-defined interfaces, allowing each layer to function independently and enabling easy modification and maintenance of the application. The 3-Tier Architecture is a widely used design pattern for building scalable and maintainable software applications, and it is commonly used in web applications and enterprise software systems.
Rules of the 3 Tier Architecture.
The term “3 Tier” cannot be applied to an application simply by dividing its code into three parts. It is crucial to follow certain rules for each tier to ensure the architecture is correctly implemented. These rules are not complex and can be easily understood.
a) Firstly, the code for each layer must be kept in separate files, which can be managed independently, possibly by different teams. Additionally, each layer should only contain code that belongs to that layer. This means that business logic should only reside in the Business layer, presentation logic in the Presentation layer, and data access logic in the Data Access layer.
b) The Presentation layer can only receive requests from and return responses to an external agent, which is typically a person but may also be another software application. It cannot have direct access to the database or the Data Access layer. Instead, it can only send requests to and receive responses from the Business layer.
c) Similarly, the Business layer can only receive requests from and return responses to the Presentation layer. It can only send requests to and receive responses from the Data Access layer, and cannot access the database directly.
d) The Data Access layer can only receive requests from and return responses to the Business layer, and cannot issue requests to anything other than the database management system (DBMS) it supports.
f) It is also important to ensure that each layer is completely unaware of the internal workings of the other layers. For instance, the Application layer must be database-agnostic and not concerned with the inner workings of the Data Access object. Similarly, it should not process data differently based on the receiving component. The Presentation layer may take the data and process it in various ways, such as constructing an HTML document, a PDF document, a CSV file, but these details should not affect the Application layer.
MVC vs 3-Tier architectures
The 3-tier architecture sounds kind of similar to a very well known architecture called MVC. Are they the same or different?
Answer: “No”.
The MVC (Model-View-Controller) and 3-Tier architectures are not the same thing, although they share some similarities. Both architectures aim to separate concerns and improve software development by dividing an application into different components.
The 3-Tier architecture as stated earlier divides an application into three layers. Each layer has its specific role, and they communicate with each other in a defined way. The Presentation layer handles user interface and input/output, the Business Logic/Application layer processes the data and implements business rules, and the Data Storage layer handles database operations.
On the other hand, the MVC architecture divides an application into three components: Model, View, and Controller. The Model represents the data and business logic, the View represents the user interface, and the Controller acts as the mediator between the Model and the View. The Controller receives input from the user, interacts with the Model to process data, and updates the View to display the results.
While both architectures aim to separate concerns and improve software development, they approach this goal in different ways. The 3-Tier architecture focuses on the separation of the different layers, while the MVC architecture focuses on the separation of components within a layer.
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