The development of Internet commercial applications and corporate Intranets around the world, which uses Java as the de facto standard language, is a significant topic in modern Software Engineering. In this context, more than ever, well-defined methodologies and high-level tools are essential for developing quality software in a way that should be as independent as possible of the changes in technology. In this article, we present an OO methodology based on a formal objectoriented model. The main feature of this method is that developers' efforts are focused on the conceptual modeling step, where analysts capture system requirements, and the full implementation can automatically be obtained following an execution model (including structure and behaviour). The final result is a web application with a three-tiered architecture, which is implemented in Java with a relational DBMS as object repository.