A large part of software development these days deals with building so-called Web applications. Many of these applications are data-base-powered and exhibit a page layout and navigational structure that is close to the class structure of the entities being managed by the system. ALso, there is often only limited application-specific business logic. This makes the usual three-tier architectural approach unappealing, because it results in a lot of unnecessary overhead. One possible solution to this problem is the use of model-driven architecture (MDA). A simple platform-independent domain describing only the entity structure of interest could be transformed into a platform-specific model that incorporates a persistence mechanism and a user interface. Yet, this raises a number of additional problems caused by the one-way, multi-transformational nature of the MDA process. To cope with these problems, the authors propose the notion of a model-driven runtime (MDR) environment that is able to execute a platform-independent model for a specific purpose instead of transforming it. The paper explains the concepts of an MDR that interprets OCL-annotated class diagrams and state machines to realize Web applications. It shows the authors' implementation of the approach, the Infolayer system, which is already used by a number of applications. Experiences from these applications are described, and the approach is compared to others.
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