1. Introduction 2. Background 3. Performance evaluation process algebra 4. Modelling study: multi-server multi-queue systems 5. Notions of equivalence 6. Isomorphism and weak isomorphism 7. Strong bisimilarity 8. Strong equivalence 9. Conclusions Bibliography Index.

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A Compositional Approach to Performance Modelling

The Palladio component model for model-driven performance prediction

Vulnerability assessment is a requirement of NERC's cybersecurity standards for electric power systems. The purpose is to study the impact of a cyber attack on supervisory control and data acquisition (SCADA) systems. Compliance of the requirement to meet the standard has become increasingly challenging as the system becomes more dispersed in wide areas. Interdependencies between computer communication system and the physical infrastructure also become more complex as information technologies are further integrated into devices and networks. This paper proposes a vulnerability assessment framework to systematically evaluate the vulnerabilities of SCADA systems at three levels: system, scenarios, and access points. The proposed method is based on cyber systems embedded with the firewall and password models, the primary mode of protection in the power industry today. The impact of a potential electronic intrusion is evaluated by its potential loss of load in the power system. This capability is enabled by integration of a logic-based simulation method and a module for the power flow computation. The IEEE 30-bus system is used to evaluate the impact of attacks launched from outside or from within the substation networks. Countermeasures are identified for improvement of the cybersecurity.

Vulnerability Assessment of Cybersecurity for SCADA Systems

In this paper we present efficient symbolic techniques for probabilistic model checking. These have been implemented in PRISM, a tool for the analysis of probabilistic models such as discrete-time Markov chains, continuous-time Markov chains and Markov decision processes using specifications in the probabilistic temporal logics PCTL and CSL. Motivated by the success of model checkers such as SMV which use BDDs (binary decision diagrams), we have developed an implementation of PCTL and CSL model checking based on MTBDDs (multi-terminal BDDs) and BDDs. Existing work in this direction has been hindered by the generally poor performance of MTBDD-based numerical computation, which is often substantially slower than explicit methods using sparse matrices. The focus of this paper is a novel hybrid technique which combines aspects of symbolic and explicit approaches to overcome these performance problems. For typical examples, we achieve a dramatic improvement over the purely symbolic approach. In addition, thanks to the compact model representation using MTBDDs, we can verify systems an order of magnitude larger than with sparse matrices, while almost matching or even beating them for speed.

http://people.cs.aau.dk/~srba/courses/FS-07/prism.pdf

Probabilistic Symbolic Model Checking with PRISM: A Hybrid Approach

Network biology is an emerging discipline that studies complex cellular processes by modeling them as networks of interactions between molecules. The analysis of biological networks presents exciting graphtheoretic and statistical problems with important applications in biology. The course will review the state-of-the-art algorithms and analysis techniques in the field, and demonstrate their applications to the study of real biological networks.

Analysis of Biological Networks

Any developer of discrete event systems knows that the most impor tant quality of the final system is that it be functionally correct by exhibiting certain functional, or qualitative properties decided upon as being important. Once assured that the system behaves correctly, it is also important that it is efficient in that its running cost is min imal or that it executes in optimum time or whatever performance measure is chosen. While functional correctness is taken for granted, the latter quantitative properties will often decide the success, or oth erwise, of the system. Ideally the developer must be able to specify, design and implement his system and test it for both functional correctness and performance using only one formalism. No such formalism exists as yet. In recent years the graphical version of the Specification and Description Lan guage (SDL) has become very popular for the specification, design and partial implementation of discrete systems. The ability to test for functional correctness of systems specified in SDL is, however, lim ited to time consuming simulative executions of the specification and performance analysis is not possible. Petri nets, although graphical in format are somewhat tedious for specifying large complex systems but, on the other hand were developed exactly to test discrete, dis tributed systems for functional correctness. With a Petri net specifi cation one can test, e. g., for deadlock, liveness and boundedness of the specified system."

Stochastic Petri Nets: An Introduction to the Theory

System analysis is often needed with respect to both qualitative and quantitative aspects. In recent decades, several formalisms have been developed that attempt to combine these aspects in one description. Present emphasis is on stochastic Petri nets. One disadvantage of these formalisms is the difficulties when describing scheduling strategies with Petri net elements. A new version of queuing Petri nets (QPNs), which combines queuing networks and Petri nets, aiming at eliminating these disadvantages is described. The new version also exhibits the modeling of timed transitions and timeless queues for describing pure scheduling mechanisms. QPNs are a superset of queueing networks and (generalized stochastic) Petri nets. The analysis of QPNs is discussed, and it is shown that efficient analysis techniques from Petri net theory can be exploited for analysis of QPNs, thus supporting the general objective of combining Petri net and queueing network formalisms. >

Queueing Petri Nets-A formalism for the combined qualitative and quantitative analysis of systems

We present a toolbox for the combined functional and quantitative analysis of discrete event dynamic systems (DEDS) on the basis of a common model interchange format, the Abstract Petri Net Notation (APNN,[5]). This format covers a fair amount of Petri net like formalisms as well as certain Queueing network concepts. At a lower level the toolbox uses a format for communicating stochastic automata, a notation to describe DEDS at a state transition level. For a more detailed description of the toolbox we refer to [3].

A Toolbox for Functional and Quantitative Analysis of DEDS

This article describes a new version of the QPN-Tool now supporting specification and analysis of hierarchically combined Queueing Petri nets (HQPNs). HQPNs are an extension of QPNs allowing the refinement of places by QPN subnets and/or queues. HQPNs can be analysed with respect to qualitative and quantitative aspects. Quantitative analysis is based on numerical Markov chain analysis. In contrast to conventional techniques the Markov chain underlying a HQPN is analysed by an approach exploiting the hierarchical structure of the model which results in a tensor representation of the generator matrix. This technique extends the size of solvable state spaces by one order of magnitude. Qualitative analysis of HQPNs relies on efficient analysis techniques based on Petri net theory. The new version of QPN-Tool implements the above analysis approaches supported by a graphical interface for a convenient specification of complex models.

QPN-Tool for the Specification ans Analysis of Hierarchically Combined Queueing Petri Nets

This paper presents a toolset for modelling and analysing logistic networks. The toolset includes a graphical user interface accommodating a "Process Chains" view. It supports model analysis by a variety of methods including simulative, algebraic and numerical techniques. An object-based, hierarchical structure helps to keep track of large models. The hierarchy employs the notion of function units which may include subordinate function units, where function units provide services to their environments that are internally accomplished by calling services of subordinate function units. This point of view is very much along the structures found in real world organisations. We describe and analyse a model of a supply chain to demonstrate the capabilities of the toolset.

Falko Bause

Papers

Stochastic Petri Nets: An Introduction to the Theory

Queueing Petri Nets-A formalism for the combined qualitative and quantitative analysis of systems

A Toolbox for Functional and Quantitative Analysis of DEDS

QPN-Tool for the Specification ans Analysis of Hierarchically Combined Queueing Petri Nets

The ProC/B Toolset for the Modelling and Analysis of Process Chains