Self-adaptation is imposing as a key characteristic of many modern software systems to tackle their complexity and cope with the many environments in which they can operate. Self-adaptation is a requirement per-se, but it also impacts the other (conventional) requirements of the system; all these new and old requirements must be elicited and represented in a coherent and homogenous way. This paper presents FLAGS, an innovative goal model that generalizes the KAOS model, adds adaptive goals to embed adaptation countermeasures, and fosters self-adaptation by considering requirements as live, runtime entities. FLAGS also distinguishes between crisp goals, whose satisfaction is boolean, and fuzzy goals, whose satisfaction is represented through fuzzy constraints. Adaptation countermeasures are triggered by violated goals and the goal model is modified accordingly to maintain a coherent view of the system and enforce adaptation directives on the running system. The main elements of the approach are demonstrated through an example application.
Web services support software architectures that can evolve dynamically. In particular, in this paper the focus is on architectures where services are composed (orchestrated) through a workflow described in the business process execution language (BPEL). It is assumed that the resulting composite service refers to external services through assertions that specify their expected functional and non-functional properties. On the basis of these assertions, the composite service may be verified at design time by checking that it ensures certain relevant properties. Because of the dynamic nature of web services and the multiple stakeholders involved in their provision, however, the external services may evolve dynamically, and even unexpectedly. They may become inconsistent with respect to the assertions against which the workflow was verified during development. As a consequence, validation of the composition must extend to run time. In this work, an assertion language, called assertion language for BPEL process interactions (ALBERT), is introduced; it can be used to specify both functional and non-functional properties. An environment which supports design-time verification of ALBERT assertions for BPEL workflows via model checking is also described. At run time, the assertions can be turned into checks that a software monitor performs on the composite system to verify that it continues to guarantee its required properties. A TeleAssistance application is provided as a running example to illustrate our validation framework
Modern software systems are often characterized by uncertainty and changes in the environment in which they are embedded. Hence, they must be designed as adaptive systems. We propose a framework that supports adaptation to non-functional manifestations of uncertainty. Our framework allows engineers to derive, from an initial model of the system, a finite state automaton augmented with probabilities. The system is then executed by an interpreter that navigates the automaton and invokes the component implementations associated to the states it traverses. The interpreter adapts the execution by choosing among alternative possible paths of the automaton in order to maximize the system's ability to meet its non-functional requirements. To demonstrate the adaptation capabilities of the proposed approach we implemented an adaptive application inspired by an existing worldwide distributed mobile application and we discussed several adaptation scenarios
Lecture Notes in Computer Science - Volume 4178/200
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