What are different types of DBMS?

Different Types of database Management System

The DBMS can be classified according to the number of users and the database site locations. These are:

On the basis of the number of users:

• Single-user DBMS
• Multi-user DBMS

 

On the basis of the site location

 

• Centralized DBMS
• Parallel DBMS
• Distributed DBMS
• Client/server DBMS

The DBMS can be  multi-user or single-user. The configuration of the hardware and also the size of the organization can confirm whether or not it's a multi-user system or one user system.

In single user system the information resides on one laptop and is just accessed by one user at a time. This one user could style, maintain, and write information programs.

Due to great deal of information management most systems square measure multi-user. during this state of affairs the information square measure each integrated and shared. A information is integrated once identical data isn't recorded in 2 places. as an example, each the Library department and also the Account department of the school information may have student addresses. despite the fact that each departments could access completely different parts of the information, the students' addresses ought to solely reside in one place. it's the work of the DBA to form positive that the software package makes the proper addresses out there from one central enclosure.

Centralized Database System

The centralized DBMS system consists of one processor along side its associated knowledge storage devices and alternative peripherals. it's physically confined to one location. knowledge will be accessed from the multiple websites with the employment of a electronic network whereas the info is maintained at the central site.

                  

Disadvantages of Centralized Database System

• When the central site computer or database system goes down, then every one (users) is blocked from using the system until the system comes back.
• Communication costs from the terminals to the central site can be expensive.

Parallel Database System

Parallel information system design consists of a multiple Central process Units (CPUs) and information storage disk in parallel. Hence, they improve process and Input/Output (I/O) speeds. Parallel information systems area unit utilized in the appliance that ought to question extraordinarily giant databases or that ought to method a particularly sizable amount of transactions per second.

Advantages of a Parallel Database System

• Parallel database systems are very useful for the applications that have to query extremely large databases (of the order of terabytes, for example, 1012 bytes) or that have to process an extremely large number of transactions per second (of the order of thousands of transactions per second).
• In a parallel database system, the throughput (that is, the number of tasks that can be completed in a given time interval) and the response time (that is, the amount of time it takes to complete a single task from the time it is· submitted) are very high.

Disadvantages of a Parallel Database System

• In a parallel database system, there· is a startup cost associated with initiating a single process and the startup-time may overshadow the actual processing time, affecting speedup adversely.
• Since process executing in a parallel system often access shared resources, a slowdown may result from interference of each new process as it completes with existing processes for commonly held resources, such as shared data storage disks, system bus and so on.

Distributed Database System

A logically interrelated collection of shared data physically distributed over a computer network is called as distributed database and the software system that permits the management of the distributed database and makes the distribution transparent to users is called as Distributed DBMS.

 

It consists of a single logical database that is split into a number of fragments. Each fragment is stored on one or more computers under the control of a separate DBMS, with the computers connected by a communications network. As shown, in distributed database system, data is spread across a variety of different databases. These are managed by a variety of different DBMS software running on a variety of different operating systems. These machines are spread (or distributed) geographically and connected together by a variety of communication networks.

                        

Advantages of Distributed Database System

 

• Distributed database architecture provides greater efficiency and better performance.

• A single database (on server) can be shared across several distinct client (application) systems.

• As data volumes and transaction rates increase, users can grow the system incrementally.

• It causes less impact on ongoing operations when adding new locations.

• Distributed database system provides local autonomy.

 

Disadvantages of Distributed Database System

 

• Recovery from failure is more complex in distributed database systems than in centralized systems.

Client-Server DBMS

Client/Server architecture of database system has two logical components namely client, and server. Clients are generally personal computers or workstations whereas server is large workstations, mini range computer system or a mainframe computer system. The applications and tools of DBMS run on one or more client platforms, while the DBMS soft wares reside on the server. The server computer is caned backend and the client's computer is called front end. These server and client computers are connected into a network. The applications and tools act as clients of the DBMS, making requests for its services. The DBMS, in turn, processes these requests and returns the results to the client(s). Client/Server architecture handles the Graphical User Interface (GUI) and does computations and other programming of interest to the end user. The server handles parts of the job that are common to many clients, for example, database access and updates.

Multi-Tier client server computing models

In a single-tier system the database is centralized, which means the DBMS Software and the data reside in one location and the dumb terminals were used to access the DBMS as shown.

                

The rise of personal computers in businesses during the 1980s, the increased reliability of networking hardware causes Two-tier and Three-tier systems became common. In a two-tier system, different software is required for the server and for the client. Illustrates the two-tier client server model. At the early stages client server computing model was called two-tier-computing model in which client is considered as data capture and validation tier and Server was considered as data storage tier. This scenario is depicted.

Problems of two-tier architecture

 

The need of enterprise scalability challenged this traditional two-tier client-server model. In the mid-1990s, as application became more complex and could be deployed to hundreds or thousands of end-users, the client side, now undergoes with following problems:

                    

• A' fat' client requiring considerable resources on client's computer to run effectively. This includes disk space, RAM and CPU.

• Client machines require administration which results overhead.

Three-tier architecture

By 1995, three-tier architecture appears as improvement over two-tier architecture. It has three layers, which are:

 

First Layer: User Interface which runs on end-user's computer (the client) .

Second Layer: Application Server It is a business logic and data processing layer. This middle tier runs on a server which is called as Application Server.

Third Layer: Database Server It is a DBMS, which stores the data required by the middle tier. This tier may run on a separate server called the database server.

As, described earlier, the client is now responsible for application's user interface, thus it requires less computational resources now clients are called as 'thin client' and it requires less maintenance.

Advantages of Client/Server Database System

1. Client/Server system has less expensive platforms to support applications that had previously been running only on large and expensive mini or mainframe computers
2. Client offer icon-based menu-driven interface, which is superior to the traditional command-line, dumb terminal interface typical of mini and mainframe computer systems.
3. Client/Server environment facilitates in more productive work by the users and making better use of existing data.
4. Client/Server database system is more flexible as compared to the Centralized system.
5. Response time and throughput is high.
6. The server (database) machine can be custom-built (tailored) to the DBMS function and thus can provide a better DBMS performance.
7. The client (application database) might be a personnel workstation, tailored to the needs of the end users and thus able to provide better interfaces, high availability, faster responses and overall improved ease of use to the user. + A single database (on server) can be shared across several distinct client (application) systems.

Disadvantages of Client/Server Database System

1. Programming cost is high in client/server environments, particularly in initial phases.
2. There is a lack of management tools for diagnosis, performance monitoring and tuning and security control, for the DBMS, client and operating systems and networking environments.