Modeling software systems with rejuvenation, restoration and checkpointing through fluid stochastic Petri nets

Speculative execution is one of the key issues to boost the performance of future generation microprocessors. In this paper, we introduce a novel approach to evaluate the effects of branch and value prediction, which allow the processor to execute instructions beyond the limits of control and true data dependences. Until now, almost all the estimations of their performance potential under different scenarios have been obtained using trace-driven or execution-driven simulation. Occasionally, some simple deterministic models have been used. We employ an analytical model based on recently introduced Fluid Stochastic Petri Nets (FSPNs) in order to capture the dynamic behavior of an ILP processor with aggressive use of prediction techniques and speculative execution. Here we define the FSPN model, derive the state equations for the underlying stochastic process and present performance evaluation results to illustrate its usage in deriving measures of interest. Our implementation-independent stochastic modeling framework reveals considerable potential for further research in this area using numerical solution of systems of partial differential equations and/or discrete-event simulation of FSPN models.

In this paper jump transitions for the fluid model part in second order fluid stochastic Petri nets (FSPNs) are introduced. The extended formalism is defined, and the underlying partial differential equations are derived. With a jump a certain amount of fluid is added to a fluid place or taken out at once. This amount, the jump height, is sampled from a probability distribution. The dynamics of a model are described by second order partial differential equations that include integrals. As examples the virtual waiting time (or unfinished work) in a queueing system and a performability model of a multi-processor system are modelled.

Stochastic Petri Net Package (SPNP) is a software package whose goal is to compute performance, availability or performability measures from Stochastic Petri Nets (SPN) and Fluid Stochastic Petri nets (FSPN). This software can use either analytic numeric methods, or simulation methods. Unfortunately, the standard discrete event simulation is inefficient to estimate the probabilities of rare events. For such rare event simulations, importance splitting technique is a good method to speedup the simulation. In the literature, two diffierent importance splitting techniques are known: RESTART and splitting. In this paper, we describe the application of these methods to (both fluid and discrete) Petri nets, their implementation in SPNP and we give some illustrations of the speed-up. The RESTART technique has already been applied in another Petri net package, TimeNet, but here we implement both RESTART and splitting, and we apply them to a more general class of Petri nets including the fluid ones.

We compare discrete-state stochastic Petri nets (SPNs) and fluid stochastic Petri nets (FSPNs) with a mixed discrete-continuous state space in their application to openloop video broadcasting systems. For both classes, we present models of the Video-on-Demand client-server system, which generally capture all relevant system aspects in a concise and graphical way. Differences in model design as well as solution techniques for various variants of these models are discussed. By simulation, we obtain measures related to blocked video playout, which allow us to evaluate customer satisfaction against bandwidth requirements. While the FSPN model has advantages in model specification and evaluation efficiency, all presented models excel in their flexibility – both in defining various performance measures and in their extensibility to include, for instance, full VCR functionality and arbitrary user behavior.

There is a need to quantify system properties methodically. Dependability and security models have evolved nearly independently. Therefore, it is crucial to develop a classification of dependability and security models which can meet the requirement of professionals in both fault-tolerant computing and security community. In this paper, we present a new classification of dependability and security models. First we present the classification of threats and mitigations in systems and networks. And then we present several individual model types such as availability, confidentiality, integrity, performance, reliability, survivability, safety and maintainability. Finally we show that each model type can be combined and represented by one of the model representation techniques: combinatorial (such as reliability block diagrams (RBD), reliability graphs, fault trees, attack trees), state-space (continuous time Markov chains, stochastic Petri nets, fluid stochastic Petri nets, etc) and hierarchical (e.g., fault trees in the upper level and Markov chains in the lower level). We show case studies for each individual model types as well as composite model types.

Modeling Hybrid Systems in SIMTHESys

What does a Heart Beat for? A Heterogeneous Approach for Human Digital Twin Construction

This paper summarizes our experiences while teaching the Models of Software Systems (MSS) course as part of the MSIT-SE master programme at Carnegie Mellon University (CMU), in Pittsburgh, PA, USA, and at Innopolis University (INNO), in Tatarstan, Russia. The MSS is a Formal Methods course taught to Software Engineers in the Fall of every year. The author was a visiting Faculty to CMU in the Fall of 2015, who then returned to Russia in the Fall of 2016 to replicate the same master course at INNO. The goal of the MSIT-SE master program at CMU as well as at INNO is to create software company leaders in the field of Software Engineering. The MSS course exposes students to several Formal Methods techniques and models, including first order logic, state machines, concurrency models and temporal logic. This paper reports our efforts to improve the quality of the MSS course by introducing the teaching of the Event-B language and its underlying software development methodology into the course programme. Our long time goal is to make Formal Methods (FM) and FM techniques more attractive to millennials and to demonstrate how they can effectively use those techniques to ensure reliability of the software systems employed by them in their IT companies.

Real-time process algebra (RTPA) is a denotational mathematical structure for denoting and manipulating system behavioral processes. RTPA is designed as a coherent algebraic system for intelligent and software system modeling, specification, refinement, and implementation. RTPA encompasses 17 metaprocesses and 17 relational process operations. RTPA can be used to describe both logical and physical models of software and intelligent systems. Logic views of system architectures and their physical platforms can be described using the same set of notations. When a system architecture is formally modeled, the static and dynamic behaviors performed on the architectural model can be specified by a three-level refinement scheme at the system, class, and object levels in a top-down approach. RTPA has been successfully applied in real-world system modeling and code generation for software systems, human cognitive processes, and intelligent systems.

Software systems start small and grow in complexity and size. The larger a software system is, the more it is distributed over organizational and geographical confines. Thus, the modeling of software systems is necessary at a certain level of complexity because it can be used for communication, documentation, configuration and certification purposes. We came to the conclusion that several patterns of software modeling exist. The existence of such patterns is dependent on the history and the evolution of the system under consideration. We will show that a software system in its lifecycle has to face several crises. Such a crisis is a watershed in the application of new patterns. We provide an evolutionary view of software systems and models which helps understanding of current problems and prospective solutions.

The available state-based and path-based reliability models for the component-based software consume high computational cost and suffer from the evaluating complexity in the software evaluation. A SVM reliability evaluation model for component-based software systems (SVMREM) with a low complexity is presented in this paper. The component reliability SVM is performed to optimize the reliability evaluation time consumption. SVMREM has a low evaluation complexity and outperforms the state-based model and the path-based model of the reliability evaluation. Another advantage of SVMREM over the others is its software structure robustness. SVMREM only depends on the component historical reliabilities, which are independent from the software system structure. Based on the theory analysis and experiment results, it shows that the SVMREM reliability evaluating accuracy is acceptable when the software system structure is complex and the complexity of SVMREM is evidently lower than the contrast models.

Reliability growth models for hardware and software systems based on nonhomogeneous Poisson processes: A survey

Many legacy systems are still essential. They run efficiently and accurately in legacy hardware and software environments. Therefore, it is necessary to migrate legacy hardware and software to modern platforms. One of the directions of migration is to service-oriented architectures. In this case, side effects are possible. Therefore, it is necessary to use the software system model. This model is used to assess the migration process of legacy software systems. An approach for building network models from the ground up is proposed in this research. Time-dependent Petri nets are used to explain the traces of events in the simulated network. A user may create a network workload model that can be utilized for network planning purposes using this technique. A method must be established to determine whether or not the created model is suitable. An example is used to determine the suitability of the Markov model for the behavior of a system with discrete states in terms of precision. An example is used to build a model for the operation of a basic software system. Providing the executable network model of the migrating system to the service identification approach input is preferred.

The paper examined the problem of modeling and design of software computer systems. The article briefly describes the content aspects of the various stages of the implementation of software complexes and systems. The methodology of research and analysis of systems, which uses the method of computer simulation modeling, is given. The aim of the work is to create a new universal approach to the design and implementation of software systems of various levels of complexity. During the study, the following general scientific methods were used: system analysis, synthesis, formalization, modeling, decomposition, structuring, description, comparison. The materials used in the study were: computers and software development tools. As a result of the study proposed a universal agent-module approach to the design and implementation of software systems based on simulation agent-based modeling. The study presents the processes of modeling and designing software systems, their stages, and the possibility of their integration within the described approach. Examples of formal model and structure of the software system under design based on the agent-module approach are presented. The proposed approach can be used in the process of software development at the initial stages related to modeling and designing of software systems. Integration of modeling and design stages in the proposed approach will significantly reduce software development time and simplify the design process by making it clearer and more formalized. Materials of the article are of scientific and practical value for a wide range of specialists interested in system analysis, modeling, design and implementation of software systems.

Modeling computer software, hardware, and other systems using Petri nets is discussed. The various analysis techniques and extension of Petri nets are considered. Problems in Petri net analysis techniques are examined, and analysis techniques that solve them are given.