A knowledge representation model which is dedicated to design applications is described. The aim is to define, implement and experiment a system supporting the dynamics of design applications, based on the object paradigm. The model draws on artificial intelligence techniques, on object-oriented programming and engineering design applications. It includes concepts found in frame-based knowledge and object-oriented representations programming languages. It also takes into account the requirements of applications that support dynamically evolving objects e.g, CAD/CAM. The requirements of engineering design applications are described first. The emphasis is on composite and evolving objects. The advantages and shortcomings of current modeling paradigms are analyzed. The object- oriented approach is specifically considered. The model SHOOD is finally described. It appears as a compromise between object- oriented concepts and knowledge representation techniques. Its ability to model design objects is detailed. The emphasis is on the support for semantic relationships, e.g dependencies between components, and for object evolution.