3-Tier Client/Server Architecture

Application (Logic) Tier (Business Logic Layer)

The application tier, also known as the business logic layer, contains the core functionalities and business rules of the application. It processes and manipulates data received from the presentation tier. This layer is responsible for validating user inputs, performing calculations, and executing business-specific operations.

Examples:

1. User Authentication: The application tier handles user login requests, verifies user credentials, and grants access to the appropriate resources based on user roles and permissions.
2. Order Processing: In an e-commerce application, the application tier manages the process of placing orders, calculating the total cost, and updating the inventory after successful orders.

Data Tier (Data Access Layer)

The data tier is the lowest layer, responsible for managing data storage and retrieval. It deals with data persistence and data access operations. It communicates with databases or external data sources to fetch or store data.

Examples:

1. Database Management System (DBMS): In a relational database system, the data tier comprises the DBMS, which stores and manages data in tables. It handles tasks such as data insertion, retrieval, modification, and deletion.
2. Data Access Object (DAO): In an object-oriented application, the data tier may include DAOs, which abstract the interactions with the database and provide methods for CRUD (Create, Read, Update, Delete) operations.

Example of Three-Tier Architecture

Let's consider an example of a web-based banking application using three-tier architecture:

Presentation Tier

1. The web browser represents the presentation tier, where users interact with the banking application.
2. The browser displays the login page with input fields for username and password.

Application (Logic) Tier

1. Once the user submits the login form, the application tier validates the user's credentials against the stored data in the database.
2. If the login is successful, the application tier retrieves the user's account information and transaction history.

Data Tier

1. The data tier contains the database that stores user account details, transaction records, and other relevant data.
2. The application tier communicates with the database to retrieve user information and perform data manipulation tasks.

Conclusion

By dividing the application into these three distinct tiers, the three-tier architecture provides a modular and organized structure, making it easier to maintain, scale, and update the application. Changes in one tier typically do not impact the other tiers, promoting better code reusability and overall system flexibility.