Client-server technology
The 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 to buildinformation processing systems based on 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 isfile server (Novell NetWare or WindowsNT Server), and they are processed on workstations through the functioning of "desktop DBMS", such as Access, Paradox, FoxPro, etc.
The DBMS is located on the workstation, andData 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 implementedthe functioning of two (at least) applications - clients and servers, which share functions among themselves. For storing and directly manipulating data, a server is responsible, for example, SQLServer, Oracle, Sybase, and others.
The user interface forms the client, inbased on the use of special tools or desktop DBMS. 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
Modification of the data is carried out by the database serverdata using a transaction mechanism that gives a 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.
Client-server technology supports thousands of users and gigabytes of information with an appropriate hardware platform.
- Security, i.e. reliable protection of information from unauthorized access.
- Flexibility. In applications working with data, allocate logical layers: user interface; rules of logical processing; Data management.
As already noted, in the file-servertechnologies all three layers are combined into one monolithic application running 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-levelthe application provides for the execution of all functions for creating a user interface on the client, and all functions for managing database information 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 your existing application to constantly changing business requirements.
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