Supervisory control with progressive events

This paper investigates some limitations of the nonblocking property when used for supervisor synthesis in discrete event systems. It is shown that there are cases where synthesis with the nonblocking property gives undesired results. To address such cases, the paper introduces progressive events as a means to specify more precisely how a synthesised supervisor should complete its tasks. The nonblocking property is modified to take progressive events into account, and appropriate methods for verification and synthesis are proposed

A process-algebraic semantics for generalised nonblocking.

Generalised nonblocking is a weak liveness property to express the ability of a system to terminate under given preconditions. This paper studies the notions of equivalence and refinement that preserve generalised nonblocking and proposes a semantic model that characterises generalised nonblocking equivalence. The model can be constructed from the transition structure of an automaton, and has a finite representation for every finite-state automaton. It is used to construct a unique automaton representation for all generalised nonblocking equivalent automata. This gives rise to effective decision procedures to verify generalised nonblocking equivalence and refinement, and to a method to simplify automata while preserving generalised nonblocking equivalence. The results of this paper provide for better understanding of nonblocking in a compositional framework, with possible applications in compositional verification

Conflict-preserving abstraction of discrete event systems using annotated automata

This paper proposes to enhance compositional verification of the nonblocking property of discrete event systems by introducing annotated automata. Annotations store nondeterministic branching information, which would otherwise be stored in extra states and transitions. This succinct representation makes it easier to simplify automata and enables new efficientmeans of abstraction, reducing the size of automata to be composed and thus the size of the synchronous product state space encountered in verification. The abstractions proposed are of polynomial complexity, and they have been successfully applied to model check the nonblocking property of the same set of large-scale industrial examples as used in related work

Progressive events in supervisory control and compositional verification

This paper investigates some limitations of the nonblocking property when used for supervisor synthesis in discrete event systems. It is shown that there are cases where synthesis with the nonblocking property gives undesired results. To address such cases, the paper introduces progressive events as a means to specify more precisely how a synthesised supervisor should complete its tasks. The nonblocking property is modified to take progressive events into account, and appropriate methods for verification and synthesis are proposed. Experiments show that progressive events can be used in the analysis of industrial-scale systems, and can expose issues that remain undetected by standard nonblocking verification

On Conflicts in Concurrent Systems

This dissertation studies conflicts. A conflict is a bug in concurrent systems where one or more components of the system may potentially be blocked from completing their task. This dissertation investigates how nonconflicting completions may be used to characterise the situations in which individual components of a system may be in conflict with other components. The first major contributions of this dissertation are new methods of abstracting systems with respect to conflicts, and showing how these methods may be used to check whether a large system is conflict-free. The second contribution is a method of comparing whether one system is less susceptible to conflict than another. The last major contribution is a method of expressing all conflicts in a system in a finite and canonical way. The methods developed have applications for model checking, refinement, and the development of contracts for concurrent systems

Three variations of observation equivalence preserving synthesis abstraction

In a previous paper we introduced the notion of synthesis abstraction, which allows efficient compositional synthesis of maximally permissive supervisors for large-scale systems of composed finite-state automata. In the current paper, observation equivalence is studied in relation to synthesis abstraction. It is shown that general observation equivalence is not useful for synthesis abstraction. Instead, we introduce additional conditions strengthening observation equivalence, so that it can be used with the compositional synthesis method. The paper concludes with an example showing the suitability of these relations to achieve substantial state reduction while computing a modular supervisor

On the use of observation equivalence in synthesis abstraction

In a previous paper we introduced the notion of synthesis abstraction, which allows efficient compositional synthesis of maximally permissive supervisors for large-scale systems of composed finite-state automata. In the current paper, observation equivalence is studied in relation to synthesis abstraction. It is shown that general observation equivalence is not useful for synthesis abstraction. Instead, we introduce additional conditions strengthening observation equivalence, so that it can be used with the compositional synthesis method. The paper concludes with an example showing the suitability of these relations to achieve substantial state reduction while computing a modular supervisor

A State-Based Characterisation of the Conflict Preorder

This paper proposes a way to effectively compare the potential of processes to cause conflict. In discrete event systems theory, two concurrent systems are said to be in conflict if they can get trapped in a situation where they are both waiting or running endlessly, forever unable to complete their common task. The conflict preorder is a process-algebraic pre-congruence that compares two processes based on their possible conflicts in combination with other processes. This paper improves on previous theoretical descriptions of the conflict preorder by introducing less conflicting pairs as a concrete state-based characterisation. Based on this characterisation, an effective algorithm is presented to determine whether two processes are related according to the conflict preorder.Comment: In Proceedings FOCLASA 2011, arXiv:1107.584

Body composition and behaviour in adult rats are influenced by maternal diet, maternal age and high-fat feeding

Fetal exposure to maternal undernutrition has lifelong consequences for physiological and metabolic function. Maternal low-protein diet is associated with an age-related phenotype in rats, characterised by a period of resistance to development of obesity in early adulthood, giving way to an obesity-prone, insulin-resistant state in later adulthood. Offspring of rats fed a control (18 % casein) or low-protein (9 % casein; LP) diet in pregnancy were challenged with a high-fat diet at 9 months of age. To assess whether other maternal factors modulated the programming effects of nutrition, offspring were studied from young (2–4 months old) and older (6–9 months old) mothers. Weight gain with a high-fat diet was attenuated in male offspring of older mothers fed LP (interaction of maternal age and diet; P = 0·011) and adipose tissue deposition was lower with LP feeding in both males and females (P < 0·05). Although the resistance to weight gain and adiposity was partially explained by lower energy intake in offspring of LP mothers (P < 0·001 males only), it was apparent that energy expenditure must be influenced by maternal diet and age. Assessment of locomotor activity indicated that energy expenditure associated with physical activity was unlikely to explain resistance to weight gain, but showed that offspring of older mothers were more anxious than thoseof younger mothers, with more rearing observed in a novel environment and on the elevated plus-maze. The data showed that in addition to maternal undernutrition, greater maternal age may influence development and long-term body composition in the rat