Debugging of Dependability Models Using Interactive Visualization of Counterexamples

Question

1. What have the authors contributed in "Debugging of dependability models using interactive visualization of counterexamples" ?

2. Why are DTMCs widely used in the modeling and analysis of stochastic systems?

3. What is the graph drawing library for yfiles?

4. What is the name of the set of vertices that have been expanded?

Accepted Answer

The authors present an approach to support the debugging of stochastic system models using interactive visualization.. The goal of this work is to facilitate the identification of causal factors in the potentially very large sets of execution traces that form counterexamples in stochastic model checking.. The authors present the application of the visualization method as implemented in their prototype tool DIPRO to two significant case studies.

Accepted Answer

Because of their conceptual simplicity, DTMCs are widely used in the modeling and analysis of stochastic systems, based on a discrete time abstraction.

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The graph drawing library yfiles [22] used in their implementation provides four layout algorithms which are suitable for incremental visualization.

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Vertices that have been expanded are called closed vertices and they are stored in the closed set, which is commonly implemented as a hash table.

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The counterexample of a probabilistic reachability property is a set X of offending paths such that the accumulated probability of X violates the probability constraint “≤ p”.

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The input processor The authorreads data from the sensors and forwards it to M. Based on this data, M sends instructions to the output processor O which controls both actuators according to the received instructions.

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The comparison of selected execution paths is a key tool in the analysis of counterexamples, as the authors shall illustrate in the following section.

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Thesecond path (Path 1) starts with IProcFail, which indicates the failure of the input processor I, followed by Timeout actions representing the unavailability of input data.

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As the authors have shown in precursory work, for a limited class of properties called probabilistic reachability it is possible to efficiently compute counterexamples using explicit state space search onthe respective Markov model.

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Selected paths can be analyzed and compared with each other by means of charts that can, for instance, display the development of the values of certain state variables along the selected paths.

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This feature and many other interaction functions allow the user to navigate through the state space, thereby learning about modeling errors during the modeling phase or about faults when debugging the model.

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The authors also work on techniques to display the counterexamples on gigapixel displays such as the Powerwall at the University of Konstanz in order to be able to visualize large excerpts of complex state spaces.

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This indicates that the most probable cause for the QoS to drop below the minimum required value are the failure of the left and the right switch, respectively.

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In order to bring out the information which paths through the graph are more relevant than others the authors define the edge width to be proportional to the f -value of the corresponding transition.

Debugging of Dependability Models Using Interactive Visualization of Counterexamples

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Most frequently asked questions

1. What have the authors contributed in "Debugging of dependability models using interactive visualization of counterexamples" ?

2. Why are DTMCs widely used in the modeling and analysis of stochastic systems?

3. What is the graph drawing library for yfiles?

4. What is the name of the set of vertices that have been expanded?

5. What is the counterexample of a probabilistic reachability property?

6. What is the function of the input processor?

7. What is the key tool in the analysis of counterexamples?

8. What is the first path in the diagram?

9. What is the definition of a probabilistic reachability property?

10. How can the user compare the state space of selected paths?

11. What is the function that allows the user to navigate through the state space?

12. What are the techniques used to display the counterexamples on gigapixel displays?

13. What is the probable cause for the QoS to drop below the minimum required value?

14. How do the authors determine the width of the graph?

Figures

Citations

Safety Analysis of an Airbag System Using Probabilistic FMEA and Probabilistic Counterexamples

Diagnosis, Synthesis and Analysis of Probabilistic Models

Counterexample Generation for Discrete-Time Markov Models: An Introductory Survey

From probabilistic counterexamples via causality to fault trees

Delta Modeling for Software Architectures.

References

Principles of Model Checking

Heuristics : Intelligent Search Strategies for Computer Problem Solving

Graph Drawing: Algorithms for the Visualization of Graphs

A logic for reasoning about time and reability

Heuristics : intelligent search strategies for computer problem solving

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