N Nikola Trcka

Branching Bisimilarity with Explicit Divergence

We consider the relational characterisation of branching bisimilarity with explicit divergence. We prove that it is an equivalence and that it coincides with the original definition of branching bisimilarity with explicit divergence in terms of coloured traces. We also establish a correspondence with several variants of an action-based modal logic with until- and divergence modalities.

Analyzing a Chi model of a turntable system using Spin, CADP, and Uppaal

Nowadays, due to increasing system complexity and growing competition and costs, industry makes high demands on powerful techniques used to design and analyze manufacturing systems. One of the most popular techniques to do performance analysis is simulation. However, simulation-based analysis cannot guarantee the correctness of a system, so it is less suitable for functional analysis. Our research focuses on examining other methods to do performance analysis and functional analysis, and trying to combine the two. One of the approaches is to translate a simulation model that is used for performance analysis to a model written in an input language of an existing verification tool. We translate a χ [D.A. van Beek, K.L. Man, M.A. Reniers, J.E. Rooda, R.R.H. Schiffelers, Syntax and Consistent Equation Semantics of Hybrid Chi, CS-Report 04-37, Eindhoven University of Technology, 2004] simulation model of a turntable system into models written in the input languages of the tools CADP [J.-C. Fernandez, H. Garavel, A. Kerbrat, L. Mounier, R. Mateescu, M. Sighireanu, CADP—a protocol validation and verification toolbox, in: Proceedings of the 8th Conference on Computer Aided Verification (CAV’96), Lecture Notes in Computer Science, vol. 1102, 1996, pp. 437–440], Spin [G.J. Holzmann, The SPIN Model Checker, Addison-Wesley, 2003] and Uppaal [K.G. Larsen, P. Pettersson, W.Yi, Uppaal in a nutshell, Int. J. Software Tools for Technology Transfer 1 (1–2) (1997) 134–152] and do a functional analysis with each of them. This allows us to evaluate the usefulness of these tools for the functional analysis of χ models. We compare the input formalisms, the expressiveness of the temporal logics, and the algorithmic techniques for model checking that are used in those tools.

Model-driven design-space exploration for embedded systems: the octopus toolset

The complexity of todays embedded systems and their development trajectories requires a systematic, model-driven design approach, supported by tooling wherever possible. Only then, development trajectories become manageable, with high-quality, cost-effective results. This paper introduces the Octopus Design-Space Exploration (DSE) toolset that aims to leverage existing modeling, analysis, and DSE tools to support model-driven DSE for embedded systems. The current toolset integrates Uppaal and CPN Tools, and is centered around the DSE Intermediate Representation (DSEIR) that is specifically designed to support DSE. The toolset architecture allows: (i) easy reuse of models between different tools, while providing model consistency, and the combined use of these tools in DSE; (ii) domain-specific abstractions to support different application domains and easy reuse of tools across domains.

Soundness verification for conceptual workflow nets with data: Early detection of errors with the most precision possible

A conceptual workflow model specifies the control flow of a workflow together with abstract data information. This model is later on refined by adding specific data information, resulting in an executable workflow which is then run on an information system. It is desirable that correctness properties of the conceptual workflow are transferable to its refinements. In this paper, we present classical workflow nets extended with data operations as a conceptual workflow model. For these nets, we develop a novel technique to verify soundness. An executable workflow is sound if from every reachable state it is always possible to terminate properly. Our technique allows us to analyze a conceptual workflow and to conclude whether there exists at least one sound refinement of it, and whether any refinement of a conceptual workflow model is sound. The positive answer to the first question in combination with the negative answer to the second question means that sound and unsound refinements for the conceptual workflow in question are possible.

Workflow soundness revisited: checking correctness in the presence of data while staying conceptual

A conceptual workflow model specifies the control flow of a workflow together with abstract data information. This model is later on refined to be executed on an information system. It is desirable that correctness properties of the conceptual workflow would be transferrable to its refinements. In this paper, we present classical workflow nets extended with data operations as a conceptual workflow model. For these nets we develop a novel technique to verify soundness. This technique allows us to conclude whether at least one or any refinement of a conceptual workflow model is sound.

Computation tree logic with deadlock detection

We study the equivalence relation on states of labelled transition systems of satisfying the same formulas in Computation Tree Logic without the next state modality (CTL-X). This relation is obtained by De Nicola & Vaandrager by translating labelled transition systems to Kripke structures, while lifting the totality restriction on the latter. They characterised it as divergence sensitive branching bisimulation equivalence. We find that this equivalence fails to be a congruence for interleaving parallel composition. The reason is that the proposed application of CTL-X to non-total Kripke structures lacks the expressiveness to cope with deadlock properties that are important in the context of parallel composition. We propose an extension of CTL-X, or an alternative treatment of non-totality, that fills this hiatus. The equivalence induced by our extension is characterised as branching bisimulation equivalence with explicit divergence, which is, moreover, shown to be the coarsest congruence contained in divergence sensitive branching bisimulation equivalence.

From Local Patterns to Global Models: Towards Domain Driven Educational Process Mining

Educational process mining (EPM) aims at (i) constructing complete and compact educational process models that are able to reproduce all observed behavior (process model discovery), (ii) checking whether the modeled behavior (either pre-authored or discovered from data) matches the observed behavior (conformance checking), and (iii) projecting information extracted from the logs onto the model, to make the tacit knowledge explicit and facilitate better understanding of the process (process model extension). In this paper we propose a new domain-driven framework for EPM which assumes that a set of pattern templates can be predefined to focus the mining in a desired way and make it more effective and efficient. We illustrate the ideas behind our approach with examples of academic curricular modeling, mining, and conformance checking, using the student database of our department.

Integrated model-driven design-space exploration for embedded systems

Embedded systems and their design trajectories are becoming increasingly complex, and there is a growing demand for performance, reliability, energy efficiency and low cost. To cope with these challenges, decision making early in the development trajectory needs to be supported by appropriate modeling and analysis. To achieve this support, we need to find the modeling abstractions that allow extensive design-space exploration, tune these modeling abstractions towards the users, and integrate support for different types of modeling and analysis.

Branching Bisimulation Congruence for Probabilistic Systems

The notion of branching bisimulation for the alternating model of probabilistic systems is not a congruence with respect to parallel composition. In this paper we first define another branching bisimulation in the more general model allowing consecutive probabilistic transitions, and we prove that it is compatible with parallel composition. We then show that our bisimulation is actually the coarsest congruence relation included in the existing branching bisimulation when restricted to the alternating model.

A Reference Model for Grid Architectures and Its Analysis

Computing and data intensive applications in physics, medicine, biology, graphics, and business intelligence require large and distributed infrastructures to address todays and tomorrows challenges. For example, process mining applications are faced with terrabytes of event data and computationally expensive algorithms. Increasingly, computer grids are used to deal with such challenges. However, despite the availability of many software packages for grid applications, a good conceptual model of the grid is missing. Grid computing is often approached in an ad-hoc and engineering-like manner. This paper provides formal description of the grid in terms of a colored Petri net (CPN). The CPN can be seen as a reference model for grids and clarifies the basic concepts at a conceptual level. Moreover, the CPN allows for various kinds of analysis ranging from verification to performance analysis. In this paper, we show that our reference model allows for the analysis of various distribution strategies using simulation.