Client-server technology

Client-server technology provides for two independent interacting processes - the server and the client, the communication between which is carried out over the network.

Servers are the processes responsible for maintaining the database and the file system, and clients are the processes that send the request and wait for the response from the server.

The client-server model is used in the construction of an information processing system based on the DBMS, as well as postal systems. There is also a so-called file-server architecture, which differs significantly from the client-server architecture.

The data in the file server system is stored on a file server (Novell NetWare or WindowsNT Server), and they are processed on workstations through the operation of "desktop DBMS", such as Access, Paradox, FoxPro, etc.

The DBMS is located on the workstation, and data manipulation is performed by several independent and inconsistent processes. All data is transferred from the server through the network to the workstation, which slows the processing speed of information.

Client-server technology is implemented by the functioning of two (at least) applications - clients and servers, which share functions among themselves. The server is responsible for storing and directly manipulating data, which can be an example of SQLServer, Oracle, Sybase and others.

The user interface is formed by a client based on the use of special tools or desktop DBMSs. Logical data processing is performed partially on the client, and partly on the server. Sending requests to the server is performed by the client, usually in the SQL language. The received requests are processed by the server, and the result is returned to the client (clients).

In this case, the data is processed in the same place where they are stored - on the server, so a large amount of them is not transmitted over the network.

Advantages of the client-server architecture

Client-server technology brings the following qualities to the information system:

• Reliability

Data modification is carried out by the database server using a transaction mechanism that gives the set of operations such properties as: 1) atomicity, which ensures data integrity at any transaction termination; 2) the independence of transactions of different users; 3) Resilience to failures - saving the results of transaction completion.

• Scalability, i.e. The ability of the system to not depend on the number of users and the amount of information without replacing the software used.

The client-server technology supports thousands of users and gigabytes of information with the appropriate hardware platform.

• Security, i.e. Reliable protection of information from unauthorized access.
• Flexibility. In applications working with data, the logical layers are distinguished: the user interface; Rules of logical processing; Data management.

As it was already mentioned, in the file-server technology all three layers are combined into one monolithic application functioning on the workstation, and all changes in the layers necessarily lead to application modification, the versions of the client and the server are different, and it is required to update the versions on all workstations .

Client-server technology in a two-tier application provides all the functions to create a user interface on the client, and all functions for managing database information are on the server, business rules can be implemented both on the server and on the client.

A three-tier application allows an intermediate layer that implements business rules that are the most variable components.

Several levels allow you to flexibly and cost-effectively adapt an existing application to constantly modifiable business requirements.