logic kết nối Có hai phương tiện cơ bản để có được kết nối hợp lý giữa máy khách và máy chủ. Một là các cuộc gọi thủ tục chương trình để chương trình trực tiếp (hoặc chương trình con) theo định nghĩa thông qua các ngôn ngữ lập trình được sử dụng. | Logical connectivity There are two basic means of obtaining logical connectivity between client and server. One is direct program-to-program procedure or subroutine calls as defined through the programming language being used. That requires that both client and server be defined on the same computing platform and linked in some manner. This mechanism was first used to provide program-to-program communication but it cannot be used when client and server are on different physical platforms. The second type of communication is the message which must be used between a client and server on different platforms and which can be used if they are on the same platform. Messages are simply a string of formatted data that identify the source and the destination address of the information being communicated the information itself and some check or control characters that indicate whether the message arrived intact. Because most C S systems are defined such that they can run on different physical platforms the use of messages to provide communications is assumed for the remainder of this discussion. Compound C S systems There are three basic differences between simple C S systems and the more complex compound C S systems. In general Compound C S systems utilize an infrastructure to provi de common services to the process-specific C S clients and servers. The infrastructure is considered in Section . Compound C S systems utilize a large number of intercommunicating servers both those that are process specific and those that provide infrastructure services. Compound C S systems utilize multiple clients that transfer information between them. As with simple systems each server in a compound system can provide multiple services. It is also possible for different infrastructure servers to incorporate and offer the same service. In that case the process implementer needs to specify the server that is going to provide a specific service. The server utilized also might .
