18th Chapter-delphi Client Server application development (i) (1)

Client/server development involves defining the client/server architecture, and then integrating the architecture with other system architectures and technologies that are critical to the implementation of the client/server. The client/sever version of Delphi 2.0 enables users to develop client/server architecture applications. In this chapter we will explain the principles of client server architecture, how to build a client/server environment with Delphi, and the programming and considerations for Delphi access to remote SQL Servers.

18.1 Delphi Client/Server application development principle

18.1.1 Client/server architecture

18.1.1.1 Architecture Overview

The customer/server system architecture has the following two features:

Is the collection of intelligent user workstations for use as an effective platform

Interoperability between platforms and software

The client/server architecture includes multiple computers that are connected to one network. Computers that process applications that request a service from another computer are called clients (client). The computer that processes the database is called the server. All users have their own computers to process the application.

The client computer can be a mainframe, a minicomputer, or a microcomputer. But because the computer has the cost advantage, therefore usually chooses them as the client. In the same way, a server is usually a microcomputer, but it can also use a mainframe or a minicomputer when a larger capacity is required. In a database environment, the client can communicate with the server through several programming interfaces called middleware (middleware). These interfaces provide connectivity between the application and the database.

Figure 18.1 Client/server architecture

Although figure 18.1 has only one server, the client/server architecture can also include multiple servers. In this case, however, each server must handle only a different database or provide a unique service. (Note: The structure of using two or more servers to handle the same database is not considered a client/server system, but rather a distributed database system)

Table 18.1 summarizes the established role of computers in client/server systems.

Table 18.1 Role of client and server computers

━━━━━━━━━━━━━━━━━━━━━━━━━━━

Client Feature Server Features

───────────────────────────

Manage user interfaces accept database requests from clients

Accept data processing database requests from users

Processes the application of logical formatting results and passes to the client

Generate Database request perform integrity check

Provide concurrent access control to the server by sending a database request

Receiving results from the server performing recovery

Formatted results optimize query and update processing

━━━━━━━━━━━━━━━━━━━━━━━━━━━

18.1.1.2 Client Overview

As noted above, the client runs programs that enable users to clarify their service requests, and transmits those requests to the server. The computations performed by the client are called front-end processing (front-end processing). Front-End processing has all the functionality associated with providing, manipulating, and displaying data.

The client software consists of network interface software, applications that support user requirements, and utilities that implement network capabilities such as e-mail (e-mail) and groupware (Groupware). Network interface software provides a variety of data transmission services. Application software performs specific tasks, such as word processing, spreadsheets, and database query generation. Utility software usually performs the standard tasks required by almost all network users.

18.1.1.3 Server Overview

The computations performed on the server are referred to as back-end processing (back-end processing). Back-end hardware (back-end hardware) is a computer that manages data resources and performs database engine functions, such as storing, manipulating, and protecting data. In a mainframe environment, the back-end network (back-end Network) provides connectivity to large computers to mass storage devices, controllers, and file servers. When you identify, evaluate, and select the appropriate server platform, you must consider the services that will be provided by the platform. For example, a database server may require fast processing capabilities. Other network services that may need to be performed are communications, applications, file access, and read-only memory (CD-ROM) services. With the wide use of new applications, the potential services that can be offered will continue to grow.

Server Software includes both network software that follows OSI or other network architectures, and applications or service software that is provided by the server to clients on the network.