A three-tier client-server DBMS architecture separates the database system into three distinct layers:

1. Presentation Layer:
   • This is the user interface layer, where users interact with the database system.
   • It handles tasks such as data entry, query formulation, and result display.
   • The presentation layer can be a web-based interface, a desktop application, or a mobile app.
2. Application Layer:
   • This layer acts as a middleman between the presentation layer and the data layer.
   • It processes user requests, performs business logic, and interacts with the database.
   • The application layer can be implemented using various programming languages and frameworks.
3. Data Layer:
   • This layer houses the actual database and its data.
   • It is responsible for data storage, retrieval, and management.
   • The data layer typically uses a database management system (DBMS) to handle these tasks.

How Three-Tier Architecture Improves Security:

1. Separation of Concerns: By separating the presentation, application, and data layers, the three-tier architecture promotes modularity and security. Changes to one layer have a minimal impact on the others, reducing the risk of vulnerabilities.
2. Centralized Data Management: The data layer is centralized, providing better control over data access and security. This makes it easier to implement security measures like encryption, access controls, and auditing.
3. Reduced Attack Surface: The presentation layer acts as a barrier between external users and the underlying database. This reduces the attack surface, making it more difficult for unauthorized users to gain access to sensitive data.
4. Improved Scalability: The three-tier architecture allows for easier scalability. If the database system experiences increased load, additional resources can be added to the data layer or application layer without affecting the presentation layer.
5. Abstraction: The application layer provides an abstraction between the presentation layer and the data layer. This makes it easier to modify the database schema or switch to a different DBMS without affecting the user interface.

In summary, the three-tier client-server DBMS architecture offers several security benefits, including separation of concerns, centralized data management, reduced attack surface, improved scalability, and abstraction. These benefits make it a popular choice for organizations that need to protect sensitive data.