Architecting Software for Complex Embedded Systems - Quality Attribute Based Approach to Openness

There has been such an increase in the complexity of systems embedded in modern industrial robots, construction equipment, cars, trains, systems in telecommunication networks etc. that the engineering of such systems requires the coordinated efforts of tens or hundreds of engineers. These engineering efforts are multidisciplinary, requiring software engineers, control engineers, hardware engineers etc. to work together in the design and implementation of the systems concerned. Many have a lifetime of 10-20 years which means that their maintenance must be carefully planned. Furthermore, most of the systems can be classified as safety-critical or dependable systems. The importance of software in complex embedded systems is increasing and software quality issues are becoming first level concerns. One of the keys to success in industry in the future will be the ability to develop high-quality embedded systems and their software on time in order to remain competitive. The complexity and size of these systems requires a systematic approach to software architecture analysis and design. To advance research in this area, we need to improve our understanding of software architecting for these systems. Among the disadvantages of current methods of software architecture design are that they target “pure” software systems and that they make simplifying assumptions that software architecture design of embedded systems begins from a well-defined, fixed list of requirements for a software subsystem. This thesis is divided into two parts and has two main objectives. In the first part, we describe the state of practice of software architecting of complex embedded systems. The objective here is to get a better understanding of the factors that influence the software architecture design of complex embedded systems. In the second part of the thesis, we study industrial robots, as open, complex embedded systems that can be extended and programmed by third party. The objective is to determine how software quality concerns and in particular dependability concerns can be systematically approached when system openness is increased. The main contributions of the thesis are the following. Several important common factors which influence the architectural design of complex embedded systems software are identified, the state of the practice is described and some areas that require further research are identified. In considering the design of open robotics system, the thesis shows which dependability means need to be applied in the architecture design phase, to support system openness. The dependability means are systematically applied within the context of software architecture approach based on quality attributes. The results presented in this thesis are based on industrial experience from the author’s work as an engineer-researcher and from systematically performed interviews with several industry experts having positions as senior architects or similar in companies that develop complex and long-lived embedded systems.