Model-driven engineering is at the forefront among recent attempts to information systems development. Models are gradually refined from domain specific descriptions to more concrete models closer to implementation. This is particularly relevant to the model transformation of collaborating business partners down to collaborating (web) services as they share a common interactional perspective. However, as requirements constantly evolve model layers change and so they have to be kept in sync. Model synchronisation keeps track of those changes and propagates them to other layers. This poster gives a brief introduction to model synchronisation as devised for the Semantic Object Model (SOM), a promising approach to model-driven service engineering. SOM allows for the gradual refinement of model layers through decomposition of business objects respective their interactional relationships.