Once, the distributed application logic needs to use a distributed object model, such as a Microsoft Distributed Component Object Model (DCOM), the Trusive Object of the Object Management Group Requests the Remote Method of Request Agent Architecture (CORBA) or SUN ( RMI). By using this basic structure, developers can still have rich resources and accuracy provided by local models and to place services in remote systems. When I already have the middleware platform (RMI, Jini, Corba, DCOM, etc.), why is it worried about web? The middleware does provide a powerful service implementation, but these systems have a common defect, that is, they cannot extend to the Internet: they require the service client to be closely coupled between the services provided by the system itself, that is, the requirements A similar basic structure. Such systems are often very fragile: if the execution mechanism of one end changes, the other end will crash. For example, if the server application is changed, the client will crash. The basic structure of tightly coupled is required, and many applications are based on this system. However, when various companies need to cooperate with each other, or when the information technology provider expands the business scope, it is difficult to achieve a single unified basic structure. You cannot guarantee the other end of the pipe that you want to communicate with it, with all the basic structures you need: the operating system, object model, or programming language it uses, you may not know anything. In contrast, web services are loosely coupled to each other. Any party in the connection can change the execution mechanism, but does not affect the normal operation of the application. From a technical point of view, people have turned to use a message-based asynchronous technique to achieve high reliability system performance, and achieve a unified connection by using XML, such as HTTP, Simple Mail Transfer Protocol (SMTP), and Important XML. The power of Web as information publisher is simple and everywhere, which is important to solve such a split middleware world. The Web provides a unified and widely applicable interface through Services that is more efficiently implemented on the traditional middleware platform, so that this platform is improved. From an N-layer application structure, the Web Service is just a package that is easy to access, and the service is still relying on the middleware. Access includes service request processing (listeners) and an interface that supports business logic operations, commercial logic itself is implemented by traditional middleware platforms. In theory, developers can integrate Web services into applications by calling the Web Application Programming Interface (API) (like calling local services), and the web API call can be sent to the remote system via the Internet. A service. For example, the Microsoft Passport service enables developers to verify an application. With PassPort service, developers can make full use of the basic structure of Passport, maintain the user database by running Passport to ensure its normal operation, regular backup, and more. The message delivery system packs the basic unit of the communication into self-description type data packets (also known as messages), and puts it in the network cable. The nature of the message delivery system and the distributed object system is that the extent to which the sender identifies the basic structure of the recipient. In a distributed system, the sender needs to speculate on the recipient's situation: how the application activates or unpacks, what kind of interface is called, and so on. On the other hand, the message delivery system creates a contract at the cable format. The sender does not need to consider the message received, and does not need to consider the communication between the two sides, the only thing to consider whether the recipient can recognize the message content. The advantages of creating a contract at the cable format are self-evident.
