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An application server's fundamental job is to provide its clients with access to what is commonly called business logic, which generates dynamic content; that is, it's code that transforms data to provide the specialized functionality offered by a business, service, or application. An application server's clients are often applications themselves, and can include web servers and other application servers. Communication between the application server and its clients might take the form of HTTP messages, but that is not required as it is for communication between web servers and their clients. Many other protocols are popular, including the variants of CGI.