Truly Concurrent Logic via In-Between Specification

AbstractIn order to obtain a formalism for the specification of true concurrency in reactive systems, we modify the μ-calculus such that properties that are valid during the execution of an action can be expressed. The interpretation of this logic is based on transition systems that are used to model the ST-semantics. We show that this logic and step equivalence have an incomparable expressive power. Furthermore, we show that the logic characterizes the ST-bisimulation equivalence for finite process algebra expressions that do not contain synchronization mechanisms

Complete abstraction through extensions of disjunctive modal transition systems

Modal transition systems and their many variants are established models for abstraction and specification as they explicitly specify necessary and possible state or behavior. Disjunctive modal transition systems can be more precise abstractions as they allow a disjunctive split on necessary transitions. We show that these abstractions are compact, sound, and complete for - and as expressive as - the modal mu-calculus if models are enriched with fairness constraints and conjunctive splitting abilities for possible transitions. We point out the potential benefits of our approach over other complete abstraction frameworks

Action Refinement in End-Based Choice Settings

The choice operator is essential for the description of action-based reactive systems. If the atomicity of actions is dropped (e.g. by action refinement), one has to decide when the choice is triggered. The standard approach is to trigger the choice when actions start. This thesis examine the alternative approach that the choice is triggered when actions terminate. This end-based choice is motivated and a process algebra, which contains an end-based choice and an action refinement operator, is established. Consistent semantics (operational, denotational, axiomatical) are given. Furthermore, the difference between the start-based and the end-based choice are examined, in particular with respect to equivalence notions. New equivalence are established, since the standard equivalences are not preserved by the end-based action refinement operator

Semantic Issues in UML 2.0 State Machines

A precise semantics for the modeling language UML 2.0 is necessary for code generation and for formal verification of models during the early stages of design. We present a formal semantics of the firing of transitions in UML 2.0 state machines. In particular, we handle shallow/deep history pseudostates, final states, join/fork pseudostates, entry/exit actions and the different kinds of transition. Furthermore, our semantics captures all orderings of actions in a run-to-completion step. We point out ambiguities and uncertainties in the UML 2.0 standard, especially in the meaning of history pseudostates and priority between transitions. We discuss different attempts in resolving these

External cost of electricity generation: contribution to the Integrated Resource Plan 2 for Electricity

The international studies on energy externalities and the local studies in South Africa suggest that the high impact areas for power generation are impacts of climate change and health impacts of outdoor air pollution. Climate change impacts are by far the greatest. The health costs due to outdoor air pollution are considered quite low based on national studies, though these may be underestimated. Damage cost from acid mine drainage is also thought to be significant, and could be substantially higher than reported here. External costs of electricity generation are a necessary factor in modelling the IRP 2. To be consistent, external costs must be added to the modeller’s reference case and to all policy cases or scenarios. In the multiple criteria decision-making process, the external costs should be reported as a distinct criterion. The weighting of this criterion relative to others (cost, carbon, and access) should be discussed with stakeholders. Although the external cost presented here are appropriate for input into the IRP 2, an extensive national review must be completed for future IRPs. Furthermore, the Integrated Energy Plan (IEP) should take additional factors into account: health impacts of indoor air pollution (important in poor households, as well as industry); noise from transport, and other poverty-related issues such as wealth impacts of paraffin fires and burns, and social costs of fuel wood scarcity

Approximation Techniques for Stochastic Analysis of Biological Systems

There has been an increasing demand for formal methods in the design process of safety-critical synthetic genetic circuits. Probabilistic model checking techniques have demonstrated significant potential in analyzing the intrinsic probabilistic behaviors of complex genetic circuit designs. However, its inability to scale limits its applicability in practice. This chapter addresses the scalability problem by presenting a state-space approximation method to remove unlikely states resulting in a reduced, finite state representation of the infinite-state continuous-time Markov chain that is amenable to probabilistic model checking. The proposed method is evaluated on a design of a genetic toggle switch. Comparisons with another state-of-art tool demonstrates both accuracy and efficiency of the presented method