Structure of Client Server Systems:In client/server architecture, clients show users who require services while servers give services. Both client and server are a combination of hardware & software. Servers are divided logical objects that communicate with clients over a network to do tasks together. A client makes a request for a service & receives a reply to that request. A server gets & processes a request, and sends back the needed response. The client/server systems may have two different types of architecture -

2-Tier and 3-Tier Client/Server Architectures

Each client/server application contains three functional units:

• Presentation logic which gives the human/machine interaction (the user interface). The presentation layer operates input from the mouse, keyboard or other input devices and gives output in the form of screen displays. For instance, the ATM machine of a bank gives such interfaces.

• Business logic is the functionality given to an application program. For instance, software that enables a customer to ask for to operate his/her balance on his/her account with the bank is business logic. It contains rules for withdrawal, for minimum balance etc. It is often known as business logic because it includes the business rules that drive a given enterprise.

• The bottom layer gives the generalized services required by the other layers including file services, communications services, print services and database services. One example of such a service may be to give the records of customer accounts.

These functional units can reside on either the client or on one or more servers in the application:

                                                                     Figure: A client-server system