The introduction of viewpoints in object-oriented environments provides a number of improvements in the modelling of complex systems, especially the use of a unique and flexible model instead of several independent sub-models. Many researchers are currently working on viewpoints in various fields of computer science, but existing approaches do not meet one's needs. The authors introduce a new relation-the visibility-and a language, called VBOOL, supporting the visibility and a set of associated mechanisms: view definition, viewpoint declaration, dynamic viewpoint evolution and consistency checking through repercussion of modifications. Their approach is illustrated by an object-oriented model of the Ariane4's vehicle equipment bay. This system has been modelled using the view based object oriented method, and simulated under Centaur.