PARTIAL ORDERS IN TRANSITION SYSTEMS FROM RESOLVABLE CONFLICT EVENT STRUCTURES

Model-checking games for fixpoint logics with partial order models

Conditional transition systems with upgrades

An abstract definition of bisimulation is presented. It enables a uniform definition of bisimulation across a range of different models for parallel computation presented as categories. As examples, transition systems, synchronisation trees, transition systems with independence (an abstraction from Petri nets) and labelled event structures are considered. On transition systems the abstract definition readily specialises to Milner's strong bisimulation. On event structures it explains and leads to a revision of history-preserving bisimulation of Rabinovitch and Traktenbrot, Goltz and van Glabeek. A tie-up with open maps in a (pre)topos, as they appear in the work of Joyal and Moerdijk, brings to light a promising new model, presheaves on categories of pomsets, into which the usual category of labelled event structures embeds fully and faithfully. As an indication of its promise, this new presheaf model has ``refinement'' operators, though further work is required to justify their appropriateness and understand their relation to previous attempts. The general approach yields a logic, generalising Hennessy-Milner logic, which is characteristic for the generalised notion of bisimulation.

In this paper, we develop an eliminating causal ambiguity approach for reactive systems with the notion of causal ambiguity, which often exists and appears in real application areas. The systems are modeled in terms of event structures with causal ambiguity. Under a certain partial order semantics, the behavior of the system can be reasoned out unambiguously. Furthermore, a variant of a linear-time equivalence termed pomset trace equivalence and a variant of a branching-time equivalence termed history preserving bisimulation equivalence based on the partial order semantics are presented. An alternative operational semantics is also discussed.

The total order assumption (TOA) is the assumption that all execution sequences of observable actions or events are totally ordered by precedence. As long as in some cases TOA is to the point, total order and partial order semantics are both legitimate but lead to different theories. I argue that TOA is a simplifying assumption, and present an example of a total order theory without interleaving, and a partial order theory with interleaving.KeywordsPartial OrderTotal OrderOrder TheoryParallel CompositionExecution SequenceThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper discusses a timed variant of a process algebra akin to LOTOS, baptized UPA, in a causality-based setting. Two timed features are incorporated—a delay function which constrains the occurrence time of atomic actions and an urgency operator that forces (local or synchronized) actions to happen urgently. Timeouts are typical urgent phenomena. A novel timed extension of event structures is introduced and used as a vehicle to provide a denotational causality-based semantics for UPA. Recursion is dealt with by using standard fixpoint theory. In addition, an operational semantics is presented based on separate time- and action-transitions that is shown to be consistent with the event structure semantics. An interleaving semantics for UPA is immediately obtained from the operational semantics. By adopting this dual approach the well-developed timed interleaving view is extended with a consistent timed partial order view and a comparison is facilitated of the partial order model and the variety of existing (interleaved) timed process algebras.

SystemC is an IEEE standard system-level language and has been widely adopted in development of embedded systems. Verifying SystemC designs is critical since it can avoid error propagation down to the final implementation. Recent works translate SystemC designs into transition systems and verify them by model checking. However, model checking suffers from the state space explosion problem. This work combines partial order reduction and symbolic model checking to combating state space explosion in verifying SystemC. Some concepts are defined to assisting in partial order reduction according to the characteristics of SystemC transition systems, and partial order reduction algorithms for symbolic model checking are presented based on these concepts. Our approach is implemented on symbolic model checker VERDS and the efficiency is demonstrated by verifying a set of SystemC designs.

Concurrent histories: A basis for observing distributed systems

Connectedness and synchronization

Recently, model checking of Petri nets based on partial order semantics w.r.t. temporal logic formulae has been extended to time Petri nets. In this paper, we present an improved algorithm for computing the McMillan-unfolding of a time Petri net which gives a finite representation of the partial order semantics and some experimental results of its implementation within the PEP tool.KeywordsPartial OrderModel CheckTemporal LogicCausal ProcessTime ExpansionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

We define net-based formal models for concurrent processes communicating by asynchronous message passing. Programs specified in an abstract language are modelled by fifo-nets with composition operators, and for the first time extended compositionality and partial order semantics are considered in the fifo-net context. This leads to an algebra of fifo-nets, together with different congruences, which extends to the asynchronous communication part of the work on CCS, TCSP and ACP.

This paper surveys various notions of equivalence for concurrent systems in the framework of Elementary Net Systems, a fundamental class in the family of Petri Net models. Two types of equivalences are considered: equivalences based on observations of actions defined in the framework of interleaving, step and partial order semantics; and equivalences based on state spaces and state observability.

We present a sound and complete compositional semantics, structured around certain abstractions of proof nets, for proof-search computation in a linear logic-based language. The model captures the interaction of agents in terms of the actions they engage into and of the dynamic creation of names. The model is adequate for reasoning about a notion of operational equivalence. We will also suggest how a partial order semantics can be derived from the present approach.

Simulation is used in the design process of dynamic systems. The results of simulation are employed for validating a model, and they are helpful for the improvement of the design of a system with respect to both, qualitative and quantitative properties. The paper concentrates on these aspects and applications of simulation in education, advocates its presence in student curricula, presents building blocks of education modules for simulation and validation with respect to both content and method, discusses requirements for simulation and validation education, and finally suggests the integration of simulation teachware in virtual classrooms and distance learning environments. Modeling and simulation is almost necessarily based on modeling languages with precise semantics. In education as well as in practice, suitable computer tools should be employed. We suggest Petri nets with sequential semantics and partial order semantics as a modeling language. The contribution is based on experiences from several university courses on system modeling and simulation with Petri nets, including practical training. Moreover, relevant concepts from recent distance learning projects are mentioned.

The heaps of pieces modelling approach (see Gaubert/Mairesse, PNPM'99) admits a (max,+)-linear model for the time consumption, under earliest firing and a given trace, of safe T-timed nets. The present paper shows that this type of model can be extended, using an appropriate partial order semantics under cluster view, to include stochastic choice and timing; we give the algorithmic construction of that semantics and obtain a semi-Markov property in multi-dimensional real time.