This paper introduces the HyDev approach to structured and systematic development of typical hypermedia applications. HyDev focuses on the early phases of the development process, i.e. analysis and design. The requirements and key aspects of the software to be built are captured with three models: an adapted domain model, an instances model and a representation model. By that means, HyDev explicitly differentiates between classes and their objects on the one hand, and between objects and their representations on the other hand. The main emphasis of this paper lies on HyDev's domain model and its domain specific classes. Keywords. hypermedia, multimedia, authoring, software engineering, requirements engineering, modeling, model-based software development