Algebraic Principles for Rely-Guarantee Style Concurrency Verification Tools

We provide simple equational principles for deriving rely-guarantee-style inference rules and refinement laws based on idempotent semirings. We link the algebraic layer with concrete models of programs based on languages and execution traces. We have implemented the approach in Isabelle/HOL as a lightweight concurrency verification tool that supports reasoning about the control and data flow of concurrent programs with shared variables at different levels of abstraction. This is illustrated on two simple verification examples

Algorithmic Analysis of Array-Accessing Programs

For programs whose data variables range over Boolean or finite domains, program verification is decidable, and this forms the basis of recent tools for software model checking. In this paper, we consider algorithmic verification of programs that use Boolean variables, and in addition, access a single array whose length is potentially unbounded, and whose elements range over pairs from Σ × D, where Σ is a finite alphabet and D is a potentially unbounded data domain. We show that the reachability problem, while undecidable in general, is (1) Pspace-complete for programs in which the array-accessing for-loops are not nested, (2) solvable in Ex-pspace for programs with arbitrarily nested loops if array elements range over a finite data domain, and (3) decidable for a restricted class of programs with doubly-nested loops. The third result establishes connections to automata and logics defining languages over data words

2-Nested Simulation is not Finitely Equationally Axiomatizable

2-nested simulation was introduced by Groote and Vaandrager [10] as the coarsest equivalence included in completed trace equivalence for which the tyft/tyxt format is a congruence format. In the lineartime-branching time spectrum of van Glabbeek [8], 2-nested simulationis one of the few equivalences for which no finite equational axiomatization is presented. In this paper we prove that such an axiomatizationdoes not exist for 2-nested simulation.Keywords: Concurrency, process algebra, basic CCS, 2-nested simulation, equational logic, complete axiomatizations

Wettbewerbsprobleme auf dem europaeischen Luftverkehrsmarkt

The present contribution starts with an inventory of the state of competition in the European air transport market and, against the backdrop of the functional deficiencies diagnosed, then focuses on the peculiarities of slot allocation. Subsequent to a presentation of suggested improvements discussed in literature, an alternative allocation procedure is described, which contains both a price component and a stochastic moment. (orig.)SIGLEAvailable from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Emptiness is Decidable for Asynchronous Cellular Machines

. We resume the investigation of asynchronous cellular automata. Originally, these devices were considered in the context of Mazurkiewicz traces, and later generalized to run on arbitrary pomsets without autoconcurrency by Droste and Gastin [DG96]. While the universality of the accepted language is known to be undecidable [Kus98], we show here that the emptiness is decidable. Our proof relies on a result due to Finkel and Schnoebelen [FS98b] on well-structured transition systems. 1 Introduction In a distributed system, some events may occur concurrently, meaning that they may occur in any order or simultaneously or even that their executions may overlap. This is the case in particular when two events use independent resources. On the other hand, some events may causally depend on each other. For instance, the receiving of a message must follow its sending. Therefore, a distributed behavior may be abstracted as a directed acyclic graph (dag), that is a set of events together wit..

History-dependent Petri nets

\u3cp\u3eMost information systems that are driven by process models (e.g., workflow management systems) record events in event logs, also known as transaction logs or audit trails. We consider processes that not only keep track of their history in a log, but also make decisions based on this log. To model such processes we extend the basic Petri net framework with the notion of history and add guards to transitions evaluated on the process history. We show that some classes of history-dependent nets can be automatically converted to classical Petri nets for analysis purposes. These classes are characterized by the form of the guards (e.g., LTL guards) and sometimes the additional requirement that the underlying classical Petri net is either bounded or has finite synchronization distances.\u3c/p\u3

Exploring an interface model for CKA

Concurrent Kleene Algebras (CKAs) serve to describe general concurrent systems in a unified way at an abstract algebraic level. Recently, a graph-based model for CKA has been defined in which the incoming and outgoing edges of a graph define its input/output interface. The present paper provides a simplification and a significant extension of the original model to cover notions of states, predicates and assertions in the vein of algebraic treatments using modal semirings. Moreover, it uses the extension to set up a variant of the temporal logic CTL* for the interface model