A brief discussion on the application classification of WEB page tool language XML (4)

4. XMLApplication classification
Generally speaking, XML applications can be divided into four categories:
　(1) Applied when customers need to interact with different data sources. The data may come from different databases, each with their own complex format. But customers interact with these databases only through one standard language, and that's XML. Due to the customizability and extensibility of XML, it is sufficient to express various types of data. After receiving the data, the customer can process it or transfer it between different databases. In short, in this type of application, XML solves the problem of unified interface of data. However, unlike other data transfer standards, XML does not define specific specifications for the occurrence of data in data files. Instead, tags are appended to the data to express the logical structure and meaning of the data. This makes XML a specification that programs can automatically understand.
　(2) It is used to distribute a large amount of computing load on the client, that is, the customer can choose and make different applications to process data according to their own needs, and the service server only needs to issue the same XML document. Still taking the above example as an example, according to the traditional "client/server" working method, the client sends different requests to the server, and the server responds respectively. This not only increases the load on the server itself, but also the network administrator must investigate various different requests in advance. In order to make different programs according to the user needs, but if the user needs are complex and changeable, it is not appropriate to still concentrate all the business logic on the server side, because the programming personnel on the server side may not have enough time to meet the requirements. There are numerous application demands, and it is too late to keep up with the changes in demand. Both parties are very passive. Using XML gives the client the initiative to process data. What the server does is to encapsulate the data into the XML file as completely and accurately as possible. Everyone gets what they need and performs their duties. The self-explanatory nature of XML enables the client to understand the logical structure and meaning of the data while receiving it, thus making extensive and general distributed computing possible.
　(3) It should be used to present the same data to different users in different appearances. This application can also be seen in the above example. It is similar to the same script, but we can express it in different forms such as TV series, movies, plays, cartoons, etc. This application will pave the way for the development of personalized and stylized web user interfaces.
　(4) Used by network agents to edit, add or delete the information obtained to meet the needs of individual users. Some customers obtain data not for direct use but to organize their own databases as needed. For example, the Ministry of Education has established a huge question bank. During the exam, the questions in the question bank are taken out to form test papers, and then the test papers are encapsulated into XML files. The next step is the most exciting part, which is passed in each school. Filter filters out all answers and then sends them to each candidate. The unfiltered content can be sent directly to the teacher. Of course, an answer compilation can also be sent after the exam. In addition, the XML file can also contain other relevant information such as difficulty coefficient, error rate in previous years, etc. In this way, with just a few small programs, the same XML file can be turned into multiple files and sent to different users.                                                                                              

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