Development processes of embedded systems have been discussed many years and there exist number of advanced development environments. A well-designed development system may give us a unified design concept but such environment consists of components provided by a single vender in most case. A mixed vender environment can pick up nice feature of each system, however the coherency of concept and operation may sacrifice. In this paper, we discuss about unification of design process based on UML methodology. We are developing prototype of Squeak/Croquet based embedded system development environment in which mixed-vender design components are integrated in unified operation style.