Dependability analysis in the early phases of UML-based system design

Computer controlled systems are used in many application fields, with different levels of criticality requirements. A common characteristic of such systems is the increasing complexity in internal structure (redundancy, layering of functionality) and operational issues (performance constraints, criticality of the controlled applications, etc.). The increasing need for effective design has contributed to push for the development of standardized and well-specified design methods and languages, which allow system developers to work with a common platform of design tools. The Unified Modeling Language (UML) [1] is a general-purpose visual modeling language that is designed to specify, visualize, construct and document aspects of object oriented systems [2,3]. UML is expected to become a de-facto standard for the design of a variety of systems from small embedded control systems to large and complex open systems. An effective design process should include an early validation of the concepts and architectural choices underlying system design. The early evaluation of system characteristics like dependability [4], performance and correctness, necessary to assess the compliance of the system under development to its targets, becomes especially important for designing systems supporting critical applications. The simultaneously increasing complexity and dependability requirements of computer controlled systems have, in fact, exposed the limits of the validation techniques traditionally used in industry, like code review, testing, fault trees or Failure Modes and Effects Analysis. Moreover, new technologies such as hardware-software co-design present new challenges for the validation process. The traditional validation techniques are being more and more complemented with advanced validation techniques, such as formal verification, model based dependability evaluation, fault injection. These techniques are not aimed to replace the traditional validation techniques, but should rather be integrated with them. The validation of designs described using UML was the