Virtual Reality (VR) is used in lots of different domains for different purposes. The technology has gained a lot of popularity during the last decennia. Together with the growing interest in VR, a lot of different software tools were developed which allow building VR applications. However, most tools available nowadays require considerable background knowledge about VR technology in order to create the desired virtual environment. It is impossible for a developer to specify the virtual environment immediately in terms of domain concepts, i.e. when creating a VR application the objects from the problem domain have to be translated into VR building blocks. This is one of the reasons why developing a VR application is complex, time-consuming and expensive.

To cope with these problems, the research group WISE at the Vrije Universiteit Brussel has developed the VR-WISE approach. This new approach for developing virtual environments introduces an explicit conceptual design phase in the development of a VR-application. As conceptual modeling introduces a mechanism to abstract from implementation details, it will reduce the complexity of developing a VR application. In addition, such an abstraction layer can also hide the specific jargon used in VR and then no special VR knowledge will be needed for making the conceptual design. Therefore, also non-technical people (like the customer or the end-user) can be involved in the development and this will improve the communication between the developers and the other stakeholders. In addition, by involving the customer more closely in the design process of the VR application, earlier detection of design flaws is possible. All this could help in realizing VR applications in a shorter time.

In this dissertation, we have focused on the conceptual modeling of complex objects. Complex objects are an important issue in VR applications. Like in the real world, objects are often composed of different parts, and the way the parts are connected influences the way the complex objects can behave. Therefore, in this dissertation we propose a set of high-level conceptual modeling concepts for specifying complex objects in the context of the VR-WISE approach. The modeling concepts proposed provide an abstraction layer on top of existing VR-primitives for connections. For all modeling concepts introduced, a graphical notation has been developed and a formal specification is defined for the syntax as well as for the semantics. The graphical notation helps in quickly building a mental model of a specified conceptual model and eases the specification of the conceptual model itself. The formal specification unambiguously defines the semantics of the different modeling concepts and therefore allows building unambiguous conceptual specifications. Furthermore, it has the advantage that it provides the basis for doing intelligent reasoning over the virtual environment. In addition, tools can be developed to assist in the translation from the conceptual specifications towards a working virtual environment. A prototype has been implemented to show the feasibility of this translation.