Client Server models

Client: It is a component which requests the server for information. For eg: PC is used in internet, workstations in LAN etc.

Server: It is a component which provides the requested information to the client. For eg. Webserver,  LAN servers etc.

Network: It is the data transmission media. The type of transmission may be request for data or data transfer. There are two types of client – server model. They are

• Two –tier model
• Three-tier model

a)Two-tier(client-Server) model:

In this model there are two major components. They are

• Front end client
• Back end server

Front end is application software which is present in the client machine. This component requests for data from the server. This contains number of drivers to connect with the different servers.

Back end is RDBMS software which is present in the server machine. This component process the requests from the client and provides the data from the database.

Disadvantages:

Client must have  a driver to access the server.If the client want to access the number of servers it should have drivers for all the servers. This is very costly because each driver carries a license fee.

Software maintenance is costly.

If the database vendors change the database design , the client must update the drivers.

b)Three-tier Client server model:

There are three major components. They are

• front end client
• back end server
• Middleware

Front end is application software which is present in the client machine. This component requests for data to the middleware. This has no drivers. Instead has a single driver to interface the middleware.

The Middleware component software process the request from the client. If it contains the requested data it sends immediately to the client. If the data requested is not present it requests the server for data. Middleware component contains number of drivers to connect with the various servers.

Back end is RDBMS software which is present in the server machine. The component process the requests from the middleware and provides the data to the middleware. The middleware sends the data to the client.

Advantages:

• Client has no drivers. So cost effective.
• If the database vendors change the database design no need to update the client software.
• Security is high.
• More than one client can request the middleware for data.