Current trends in web development still are attached to the web page paradigm. Nevertheless, new uses of already available technology and recent development in terms of concepts, as the asynchronous communication, have produced a new generation of web applications: Rich Internet Applications (RIAs). These web applications tries to fulfill user expectations in terms of usability, reliability, quality, maintainability and performance. In our work, we are going to present a design methodology that pursued as goal describing and developing User Interfaces of RIAs in a standardized way. Author Keywords Rich internet applications, web engineering, Model driven engineering, USIXML. ACM Classification Keywords H.5.4. Hypertext/Hypermedia: User Issues. H.5.m. Information interfaces and presentation (e.g., HCI): Miscellaneous. General Terms Management, Design, Human Factors