In the SIRENA project, the service oriented approach is used to connect devices using Web services or Universal Plug and Play (UPnP). In this environment, resources are scarce, and near real time behaviour and high reliability without user intervention is needed. At least in our context an interface design for service oriented architecture should not use a classical object oriented method decomposition and export these methods as service actions, although this approach is suggested by corresponding tool support. This is not only be highly inefficient, but very often ignores the unreliability because of the real concurrency that is always present in networked applications. The article analyses the possible problems in interface design for service oriented control, explains differences to object oriented programming and refers to well-known techniques to avoid the issues described