DBMS - Centralized and Client-Server Architecture

When studying Database Management Systems (DBMS), it's essential to understand the different architectures they can follow. The architecture of a DBMS determines how the data is stored, processed, and accessed by users. In this chapter, we will explore centralized and client-server DBMS architectures, along with their key features and examples for better understanding.

Centralized DBMS Architecture

A centralized system operates through a central node. In a centralized DBMS architecture, all database operations, user interfaces, and applications are managed by a single central computer typically a mainframe or a powerful server.

This type of architecture was common in the early days of computing, when most processing power resided in a central location. Users would access the mainframe through terminals connected via a network. These terminals had minimal processing capabilities and served primarily as input/output devices.

Working of Centralized DBMS Architecture

All user interactions in a centralized DBMS take place through the terminals. Terminals are some basic interfaces connected to the mainframe. These terminals do not process the data themselves. They send the input commands to the server. The command handles the execution. The server processes the commands and returns the results to the terminals for display.

Let's understand this with an example. Consider a university that uses a centralized DBMS to manage its student database. All student-related queries such as checking grades or registering for classes are processed on a central mainframe. Terminals located across the campus send requests to this central server, which processes the queries, retrieves the required data, and sends the results back to the terminals for display.

Centralized DBMS Architecture - Benefits and Drawbacks

The following table highlights the benefits and drawbacks of using a centralized DBMS architecture −

Client-Server DBMS Architecture

The client-server system is evolvement of centralized system. This architecture divides the workload between clients (user-facing systems) and servers (back-end systems). The clients handle the user interface and local processing. It is the servers manage data storage, complex processing, and business logic.

Basic Structure of Client-Server Architecture

In its simplest form, the client-server model has the following objects:

• Clients: Machines or software applications where the users interact. These handle user inputs and present results.
• Servers: Systems that store the database and execute data processing tasks.

For example, a customer service platform where employees use desktop computers (clients) to access a centralized customer database (server). The client computers send queries to the server, which processes them and returns the necessary information.

Distributing the workload between client and server helps balance resource use and reduces the load on a single system. Clients and servers can be located on different machines, facilitating remote access and distributed data processing.

Two-Tier Client-Server Architecture

In a two-tier client-server architecture, the client handles the user interface and application logic. On the other hand the server focuses on data storage and retrieval. The connection between the client and the server allows clients to submit requests (queries). The queries uses the server processes and returns as results.

For example, a banking application where tellers use client-side software to check account balances. The client software connects to a centralized database server, retrieves data, and displays it on the teller's screen.

Client-Server DBMS Architecture − Benefits and Drawbacks

The following table highlights the benefits and drawbacks of client-server DBMS architecture −

Three-Tier Client-Server Architecture

The speciality of three-tier architecture is that, it has an additional layer between the client and the server. This is known as application server. This intermediate layer helps manage business logic, application rules, and data processing more effectively.

Following are the components of three-tier client-server DBMS architecture −

• Presentation Layer (Client) − Displays data and collects user input.
• Application Layer (Middle Tier) − Processes user requests and interacts with the database.
• Data Layer (Server) − Handles database storage and management.

Example − A web-based ordering system for a restaurant. The client (user's web browser) interacts with a web server (application layer), which processes orders and retrieves data from the database server (data layer). This structure allows for better load distribution and supports complex business logic.

Following are the advantages of using three-tier client-server DBMS architecture −

• Better Load Management − The middle tier processes requests before sending them to the database server, reducing the server's direct load.
• Enhanced Security − The application server acts as a gatekeeper, validating user requests and providing controlled database access.

For example, in a healthcare information system, patient data can be accessed securely by separating user-access from direct database interaction through an application server. This improves the security by ensuring sensitive data is only accessible to authenticated users.

Beyond Three Tiers: n-Tier DBMS Architectures

Three-tier systems are common, some applications extend it to n-tier architectures. Such architectures can include additional processing layers for more specialized tasks such as separate layers for authentication, data aggregation, or specific application services.

Example − Large enterprise applications, like those used in CRM or ERP, often utilize n-tier structures to balance tasks across various layers.

Following are the benefits of using n-tier systems −

• Modularity − Breaking down the application into multiple layers allows teams to develop and manage parts independently.
• Resilience − Failures in one layer can be managed without affecting the entire system, which greatly enhances reliability.

Conclusion

In this chapter, we touched upon the concept of centralized and client-server architectures for DBMS. We understood how a centralized DBMS relies on a single mainframe, while a client‑server models distribute tasks between user-facing clients and back-end servers.

The transition to two-tier and three-tier architectures has allowed for greater flexibility, better performance, and improved security. We also highlighted the features of n-tier architectures, which further distribute tasks for enhanced scalability and resilience.