MOSES: Modular modelling of physical systems in an object-oriented database. The article describes MOSES, a new software environment conceived for the object-oriented modelling of physical systems. The most original aspect of MOSES is the adoption of an object-oriented database as the support of the modelling environment, that allows full treatment of complex model objects as data objects. It is shown how this choice is compliant with the basic requirements of Computer Aided Engineering of complex technological systems. Examples in the field of robotics are discussed.