Abstract4Designing and implementing Web Services constitutes a large and constantly growing part of the information technology market.Web Services have specific scenarios in which distributed processes and network resources are used.This aspect of services requires integration with the model checkers.This article presents the experimentation framework in which services can be specified and then formally analyzed for deadlock-freedom, achievement of process goals, and similar features.Rybu4WS language enriches the basic Rybu language with the ability to use variables in processes, service calls between servers, new structural instructions, and other constructions known to programmers while remaining in line with declarative, mathematical IMDS formalism.Additionally, the development environment allows simulation of a counterexample or a witness -obtained as a result of the model checking -in a similar way to traditional debuggers.

Abstract Automated verification of distributed systems becomes very important in distributed computing. The graphical insight into the system in the early and late stages of the project is essential. In the design phase, the visual input helps to articulate the collaborative distributed components clearly. The formal verification gives evidence of correctness or malfunction, but in the latter case, graphical simulation of counterexample helps for better understanding design errors. For these purposes, we invented Distributed Autonomous and Asynchronous Automata (DA3), which have the same semantics as the formal verification base—Integrated Model of Distributed Systems (IMDS). The IMDS model reflects the natural characteristics of distributed systems: unicasting, locality, autonomy, and asynchrony. Distributed automata have all of these features because they share the same semantics as IMDS. In formalism, the unified system definition has two views: the server view of the cooperating distributed nodes and the agent view of the migrating agents performing distributed computations. The automata have two formally equivalent forms that reflect two views: Server DA3 for observing servers exchanging messages, and Agent DA3 for tracking agents, which visit individual servers in their progress of distributed calculations. We present the DA3 formulation based on the IMDS formalism and their application to design and verify distributed systems in the Dedan environment. DA3 formalism is compared with other concepts of distributed automata known from the literature.

Automated transit networks (ATN) are subject to intensive research. Many models of ATN systems have been analyzed and many features have been studied. However, most paper use a single benchmark, test selected features, and use author's own measures for the network itself and its operation. This paper presents several benchmarks of ATN systems and their characteristics being the subject of research. We show that general measures are rarely used to assess network size, its regularity, demand structure, and traffic parameters. We also show that scalar variables are not used for comparison, which makes them doubtful. We propose a set of measures for several of the most important features of ATN systems. They are generally based on scalars elaborated using square measures and entropy. Such a set of measures may be used to compare various benchmarks and their performance.

Integrated Model of Distributed Systems (IMDS) is a formalism for specification and verification of distributed systems, especially following IoT (Internet of Things) paradigm.The formalism emphasizes such features as asynchrony of actions and communication, locality of decisions, and autonomy in executing actions.In conjunction with model checking, IMDS allows to analyze such features of distributed systems as deadlocks or distributed termination.However, the nature of model checking allows to find one deadlock in a single run of the verifier, which produces a counterexample.The conversion of IMDS specification to a Petri net is used to identify multiple deadlocks in one verification, using siphons.Model checking is used to verify if a siphon can become empty, which denotes a true deadlock in a purely cyclic system, like FMS (Flexible Manufacturing Systems).The extension of the verification by temporal checking allows to cover systems with any structure: cyclic, terminating, or with a more complex scheme.In addition, the proposed procedure allows to easily identify processes participating in partial deadlocks.Two types of deadlock can be identified: communication deadlocks and resource deadlocks.

Modern static deadlock detection techniques deal with the global properties of the verified systems, using methods that explore the state space. Local features, like partial deadlocks or individual process terminations, are not easily expressed or checked by such methods. Also the distinction between communication deadlocks and resource deadlocks, common in dynamic waits-for methods, cannot be addressed or verified by static methods. An Integrated Model of Distributed Systems (IMDS) is proposed which specifies distributed systems as sets of servers’ states, sets of messages and sets of actions. The message passing/resource sharing dualism of distributed systems is provided by projections: on servers (server view) and on agents (agent view), yet the uniform specification of a verified system is preserved. A progress of computation is defined in terms of actions which change (local) states and generate messages. Distributed actions do not depend on global states and are independent from one another. Therefore, local features of subsystems can be easily described in IMDS. Communication and resource deadlocks can be handled separately and total and partial deadlocks and terminations can be distinguished from each other. Integration of IMDS with model checking is outlined and temporal formulas for deadlock and termination checking are discussed.

Classical algorithms of evaluation of temporal CTL formulas are constructed "bottom-up". A formula must be evaluated completely to give the result. In the paper, a new concept of "top-down" evaluation of temporal QsCTL (CTL with state quantifiers) formulas, called "Checking By Spheres" is presented. The new algorithm has two general advantages: the evaluation may be stopped on certain conditions in early steps of the algorithm (not the whole formula and not whole state space should be analyzed), and state quantification may be used in formulas (even if a range of a quantifier is not statically obtainable).

The aim of this paper is to demonstrate how the COSMA environment can be used for system modeling. This environment is a set of tools based on concurrent state machines paradigm and is developed in the Institute of Computer Science at the Warsaw University of Technology. Our demonstration example is a distributed brake control system dedicated for a railway transport. The paper shortly introduces COSMA. Next it shows how the example model can be validated by our temporal logic analyzer.

Many new multi-microprocessor systems are available or have been announced to the market. A method of structured operating-system construction to present a distributed hardware environment as a single computer to the user is proposed. Unlike many existing distributed operating systems, which are parallel and process-oriented, the new approach is based on a hierarchical structure of layers. The concept permits the designer to establish almost any dependencies between local operating systems. A distribution of Unix-like systems in a heterogeneous multi-microprocessor -environment-is proposed.