Model-Driven Engineering (MDE) advocates the generation of software applications from models, which are views on certain aspects of the software. In order to minimize the delta between these views we propose a highly dynamic Round-Trip Engineering (RTE) technique where the elements of the various views are one and the same. We combine Extended Entity-Relationship diagrams with an object-oriented prototype-based language in a two-phased technique that allows for the rapid prototyping of the modeled applications. Run-time objects are included in the RTE process resulting in advanced constraint enforcement. Moreover support is provided for straightforward role modeling.