In this paper we present the experiences and architecture from a research project conducted in cooperation with two industry partners. The goal of the project was to reengineer an existing system for haemo dialysis machines into a domain specific software architecture [22]. Our main experiences are (1) architecture design is an iterative and incremental process, (2) software qualities require a context, (3) quality attribute assessment methods are too detailed for use during architectural design, (4) application domain concepts are not abstractions, (5) aesthetics guides the architect in finding potential weaknesses in the architecture, (6) it is extremely hard to decide when an architecture design is ready, and (7) documenting software architectures is a important problem. We also present the architecture and the design rational to give a basis for our experiences. We evaluated the resulting architecture by implementing a prototype application. Keywords Software Architecture, Softwar...