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## A Combined Toolset for the Verification of Real-Time Distributed Systems

Checking the correctness of distributed systems is one of the most difficult and urgent problems in software engineering. A combined toolset for the verification of real-time distributed systems (RTDS) is described. RTDSs are specified as statecharts in the Universal Modeling Language (UML). The semantics of statecharts is defined by means of hierarchical timed automata. The combined toolset consists of a UML statechart editor, a verification tool for model checking networks of real-time automata in UPPAAL, and a translator of UML statecharts into networks of timed automata. The focus is on the translation algorithm from UML statecharts into networks of hierarchical timed automata. To illustrate the proposed approach to the verification of RTDSs, a toy example of a real-time crossroad traffic control system is analyzed.

This volume contains the Proceedings of 22nd Concurrency, Specification and Programming (GS&P) Workshop held on September 25-27, 2013 in Warsaw. There were 48 submissions. Each submission was reviewed by two program committee members. The committee decided to accept 40 papers. The Workshop was initiated in the mid 1970s by computer scientists and mathematicians from Warsaw and Humboldt Universities, as Polish-German annual meetings. They were suspended for some years in the 1980s and reactimed in 1992. Thereafter, the Workshop, organised alternatingly by the Institutes of Informatics and Mathematics of the University of Warsaw and the Institute of Informatics of Humboldt University in Berlin on the basis of an exchange program, has been given the name GS&P. It should be mentioned that the CS&P meetings, initially purely bilateral, since 1992 have developed into events attended by participants from a number of different countries beside Poland and Germany. The present GS&P'13 meeting attracted contributors from: Canada, Egypt, France, Germany, Italy, Nepal, The Netherlands, Poland, Russia, Serbia, Slenakia, Sweden, Turkey, United Kingdom, United States, and Vietnam. The organisation of this year's CS&P would not be possible without the resources and financing provided by seven institutions. We would like to thank the Faculty of Mathematics, Informatics and Mechanics of the University of Warsaw and the Institute of Informatics of the Humboldt University of Berlin for the continuing financial and organisational support provided to GS&P over last twenty-two years. The essential financial backing received from the Warsaw Center of Mathematics and Computer Science made the organisation of CS&P 2013 possible. Our thanks go to the Bialystok University of Technology for providing the means for publishing this proceedings volume. Last, but not the least, we are grateful for the significant financial support provided by the Vistula University in Warsaw.

This volume contains the papers presented at CS&P 2014: 23th International Workshop on Concurrency, Specification and Programming held on September 28 - October 1, 2014 in Chemnitz. Since the early seventies Warsaw University and Humboldt-University have alternately organized an annual workshop - since 1993 as CS&P. Over time, it has grown from a bilateral seminar to a meeting attended also by colleagues from other countries than Poland and Germany. This year there are 34 participants from 10 countries.

In this article, we investigate the logical structure of memory models of theoretical and practical interest. Our main interest is in “the logic behind a fixed memory model”, rather than in “a model of any kind behind a given logical system”. As an effective language for reasoning about such memory models, we use the formalism of separation logic. Our main result is that for any concrete choice of heap-like memory model, validity in that model is *undecidable* even for purely propositional formulas in this language.

The main novelty of our approach to the problem is that we focus on validity in specific, concrete memory models, as opposed to validity in general classes of models.

Besides its intrinsic technical interest, this result also provides new insights into the nature of their decidable fragments. In particular, we show that, in order to obtain such decidable fragments, either the formula language must be severely restricted or the valuations of propositional variables must be constrained.

In addition, we show that a number of propositional systems that approximate separation logic are undecidable as well. In particular, this resolves the open problems of decidability for Boolean BI and Classical BI.

Moreover, we provide one of the simplest undecidable propositional systems currently known in the literature, called “Minimal Boolean BI”, by combining the purely positive implication-conjunction fragment of Boolean logic with the laws of multiplicative *-conjunction, its unit and its adjoint implication, originally provided by intuitionistic multiplicative linear logic. Each of these two components is individually decidable: the implication-conjunction fragment of Boolean logic is co-NP-complete, and intuitionistic multiplicative linear logic is NP-complete.

All of our undecidability results are obtained by means of a direct encoding of Minsky machines.

Key Words and Phrases: Separation logic, undecidability, memory models, bunched logic

The specification-based approach is widely used for test program generation for functional verification of microprocessors. The size of microprocessor specifications is measured in thousands lines of code. Consequently, their maintenance requires significant effort. Typical maintenance activities include regular updates, substitution of deprecated functionality, and support for new revisions and implementation-defined features. Our team is working on MicroTESK, a tool that generates test programs for microprocessors based on specifications of the instruction set architectures. The specifications are created in a specialized language, called nML, extended with facilities to manage revision-specific and implementation-defined features. The tool has been applied to ARMv8, MIPS64, PowerPC, RISC-V, and x86 microprocessors. This paper describes our experience in maintaining specifications and the approach we use to simplify this process.

Coordination of several distributed system components is an error-prone task, since interaction of several simple components can generate rather sophisticated behavior. Verification of such systems is very difficult or even impossible because of the so-called state space explosion problem, when the size of the system reachability set grows exponentially on the number of interacting agents. To overcome this problem several approaches to construct correct models of interacting agents in a compositional way were proposed in the literature. They define different properties and conditions to ensure correct behavior of interacting agents. Checking these conditions may be in its turn quite a problem. In this paper, we propose patterns for correct composition of component models. For justifying these patterns we use special net morphisms. However, to apply patterns the user does not need to be familiar with the underlying theory.

Workshop on Program Semantics, Specification and Verification: Theory and Applications is the leading event in Russia in the field of applying of the formal methods to software analysis. Proceedings of the fourth workshop are dedicated to formalisms for program semantics, formal models and verication, programming and specification languages, etc.

The paper proposes a method of automated construction of behavior models of microprocessors, which are used in the process of test program generation to predict the results. The proposed method is based on using formal specifications of instruction set architecture. The method is implemented in MicroTESK, a test program generation tool being developed at ISP RAS. The tool has been successfully applied in industrial projects.

Software-dened networking (SDN) is an approach to building computer net- works that separate and abstract data planes and control planes of these systems. In a SDN a centralized controller manages a distributed set of switches. A set of open commands for packet forwarding and ow-table updating was dened in the form of a protocol known as OpenFlow. In this paper we describe an abstract formal model of SDN, introduce a tentative language for specication of SDN forwarding policies, and set up formally model-checking problems for SDNs.

Nested Petri nets is an extension of Petri net formalism with net tokens for modelling multi-agent distributed systems with complex structure. Temporal logics, such as CTL, are used to state requirements of software systems behaviour. However, in the case of nested Petri nets models, CTL is not expressive enough for specification of system behaviour. In this paper we propose an extension of CTL with a new modality for specifying agents behavior. We define syntax and formal semantics for our logic, and give small examples of its usage.

A model for organizing cargo transportation between two node stations connected by a railway line which contains a certain number of intermediate stations is considered. The movement of cargo is in one direction. Such a situation may occur, for example, if one of the node stations is located in a region which produce raw material for manufacturing industry located in another region, and there is another node station. The organization of freight traﬃc is performed by means of a number of technologies. These technologies determine the rules for taking on cargo at the initial node station, the rules of interaction between neighboring stations, as well as the rule of distribution of cargo to the ﬁnal node stations. The process of cargo transportation is followed by the set rule of control. For such a model, one must determine possible modes of cargo transportation and describe their properties. This model is described by a ﬁnite-dimensional system of diﬀerential equations with nonlocal linear restrictions. The class of the solution satisfying nonlocal linear restrictions is extremely narrow. It results in the need for the “correct” extension of solutions of a system of diﬀerential equations to a class of quasi-solutions having the distinctive feature of gaps in a countable number of points. It was possible numerically using the Runge–Kutta method of the fourth order to build these quasi-solutions and determine their rate of growth. Let us note that in the technical plan the main complexity consisted in obtaining quasi-solutions satisfying the nonlocal linear restrictions. Furthermore, we investigated the dependence of quasi-solutions and, in particular, sizes of gaps (jumps) of solutions on a number of parameters of the model characterizing a rule of control, technologies for transportation of cargo and intensity of giving of cargo on a node station.

Event logs collected by modern information and technical systems usually contain enough data for automated process models discovery. A variety of algorithms was developed for process models discovery, conformance checking, log to model alignment, comparison of process models, etc., nevertheless a quick analysis of ad-hoc selected parts of a journal still have not get a full-fledged implementation. This paper describes an ROLAP-based method of multidimensional event logs storage for process mining. The result of the analysis of the journal is visualized as directed graph representing the union of all possible event sequences, ranked by their occurrence probability. Our implementation allows the analyst to discover process models for sublogs defined by ad-hoc selection of criteria and value of occurrence probability

Existing approaches suggest that IT strategy should be a reflection of business strategy. However, actually organisations do not often follow business strategy even if it is formally declared. In these conditions, IT strategy can be viewed not as a plan, but as an organisational shared view on the role of information systems. This approach generally reflects only a top-down perspective of IT strategy. So, it can be supplemented by a strategic behaviour pattern (i.e., more or less standard response to a changes that is formed as result of previous experience) to implement bottom-up approach. Two components that can help to establish effective reaction regarding new initiatives in IT are proposed here: model of IT-related decision making, and efficiency measurement metric to estimate maturity of business processes and appropriate IT. Usage of proposed tools is demonstrated in practical cases.