The connection between an event structure semantics and an operational semantics for TCSP

The relation between an operational interleaving semantics for TSCP based on a transition system and a compositional true concurrency semantics based on event structures is studied. In particular we extend the consistency result of U. Goltz and R. Loogen [Ann. Soc. Math. Pol., Ser. IV, Fundam. Inf. 14, 39-73 (1991; Zbl 0717.68028)] for TCSP processes without recursion to the general case. Thus, we obtain for every TCSP process P that its operational meaning O(P) and the interleaving behaviour O(M[[P]]) which is derived from the event structure M[[P]] associated with P are bisimilar. (aus: Zentralblatt MATH

Tools and verification techniques for integrated formal methods

Ph.DDOCTOR OF PHILOSOPH

Constrained shortest paths for QoS routing and path protection in communication networks.

The CSDP (k) problem requires the selection of a set of k > 1 link-disjoint paths with minimum total cost and with total delay bounded by a given upper bound. This problem arises in the context of provisioning paths in a network that could be used to provide resilience to link failures. Again we studied the LP relaxation of the ILP formulation of the problem from the primal perspective and proposed an approximation algorithm.We have studied certain combinatorial optimization problems that arise in the context of two important problems in computer communication networks: end-to-end Quality of Service (QoS) and fault tolerance. These problems can be modeled as constrained shortest path(s) selection problems on networks with each of their links associated with additive weights representing the cost, delay etc.The problems considered above assume that the network status is known and accurate. However, in real networks, this assumption is not realistic. So we considered the QoS route selection problem under inaccurate state information. Here the goal is to find a path with the highest probability that satisfies a given delay upper bound. We proposed a pseudo-polynomial time approximation algorithm, a fully polynomial time approximation scheme, and a strongly polynomial time heuristic for this problem.Finally we studied the constrained shortest path problem with multiple additive constraints. Using the LARAC algorithm as a building block and combining ideas from mathematical programming, we proposed a new approximation algorithm.First we studied the QoS single route selection problem, i.e., the constrained shortest path (CSP) problem. The goal of the CSP problem is to identify a minimum cost route which incurs a delay less than a specified bound. It can be formulated as an integer linear programming (ILP) problem which is computationally intractable. The LARAC algorithm reported in the literature is based on the dual of the linear programming relaxation of the ILP formulation and gives an approximate solution. We proposed two new approximation algorithms solving the dual problem. Next, we studied the CSP problem using the primal simplex method and exploiting certain structural properties of networks. This led to a novel approximation algorithm

Combined Modeling of Software and Hardware with Versions and Variants

Produktlinien ermöglichen die Entwicklung variabler, konfigurierbarer Produkte auf Basis von Konfigurationen. Eine valide Konfiguration wird im Problemraum einer Produktlinie abgeleitet, während ihre Realisierbarkeit zu einem Produkt im Lösungsraum entschieden wird. Eine valide, aber nicht realisierbare Konfiguration führt zu einer Inkonsistenz zwischen Problem- und Lösungsraum, da die Menge der tatsächlich baubaren Produkte im Lösungsraum nicht mit der definierten Variabilität im Problemraum übereinstimmt. Für große Produktlinien ist es händisch schwierig zu entscheiden, ob Inkonsistenzen existieren, da die Anzahl der Konfigurationen in Produktlinien exponentiell wächst. In dieser Arbeit wird die Konsistenz von Problem- und Lösungsraum adressiert und zwei formale Methoden auf Basis von Bedingungserfüllungsproblemen vorgeschlagen, um die Menge der Konfigurationen zu berechnen, die sowohl valide als auch realisierbar sind. Die Sampling-Methode entscheidet die Realisierbarkeit für jede Konfiguration aus einer Menge von validen Konfigurationen einzeln. Damit kann im Voraus überprüft werden, welche bestehenden Konfigurationen auch nach einer Softwareaktualisierung noch funktionsfähig sind. Die kombinierte Methode berechnet direkt Konfigurationen, die sowohl valide als auch realisierbar sind, für weitere Produkttests. Beide Methoden werden anhand zweier Fallstudien mit exemplarischen Produktlinien evaluiert. In den Ergebnissen wird gezeigt, dass beide Methoden alle Inkonsistenzen zwischen Problem- und Lösungsraum in den Produktlinienbeispielen identifizieren können

A theory of processes with durational actions

AbstractA new bisimulation based semantics, called performance equivalence, is proposed for a process algebra equipped with the TCSP parallel operator. This semantics relies on the basic assumption that actions are time-consuming, where their duration is statically fixed. Performance equivalence equates systems whenever they perform the same actions in the same amount of time, thus introducing a simple form of performance evaluation in process algebras. A comparison with other equivalences is provided; in particular, we show that performance equivalence is strictly finer than step bisimulation equivalence and strictly coarser than partial ordering bisimulation equivalence

Further Results on Partial Order Equivalences on Infinite Systems

In [26], we investigated decidability issues for standard language equivalence for process description languages with two generalisations based on traditional approachesfor capturing non-interleaving behaviour: pomset equivalence reflecting global causal dependency, and location equivalence reflecting spatial distribution of events. In this paper, we continue by investigating the role played by TCSP-style renaming and hiding combinators with respect to decidability. One result of [26] was that in contrast to pomset equivalence, location equivalence remained decidable for a class of processes consisting of finite sets of BPP processes communicating in a TCSP manner. Here, we show that location equivalence becomes undecidable when either renaming or hiding is added to this class of processes. Furthermore, we investigate the weak versions of location and pomset equivalences.We show that for BPP with prefixing, both weak pomset and weak location equivalence are decidable. Moreover, we show that weak location equivalence is undecidable for BPP semantically extended with CCS communication

Musings on Encodings and Expressiveness

This paper proposes a definition of what it means for one system description language to encode another one, thereby enabling an ordering of system description languages with respect to expressive power. I compare the proposed definition with other definitions of encoding and expressiveness found in the literature, and illustrate it on a case study: comparing the expressive power of CCS and CSP.Comment: In Proceedings EXPRESS/SOS 2012, arXiv:1208.244