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Access provided by: anon Sign Out. GUARDS: a generic upgradable architecture for real-time dependable systems Abstract: The development and validation of fault-tolerant computers for critical real-time applications are currently both costly and time consuming. It also defines new dependability specific types either as specialization of basic NFP types e.
A Petri net PN —shown in Figure 9 —is a bipartite graph, in which the vertices can be either transitions or places.
The transitions, graphically depicted by bars, represent events that may occur in the system; the places, represented by circles, are used to model conditions. The directed arcs, shown by arrows, describe which places are pre- or postconditions for which transitions. Places may contain tokens, depicted by black dots; the initial distribution of tokens over the places of a PN is called initial marking. The PN dynamics is governed by the transition enabling and firing rules.
A transition is enabled whenever there is at least a token in each of its precondition places, and it may fires if there are not enabled transitions with higher priority. When it fires, a token is consumed from each of its precondition places and a token is produced in each of its postcondition places see Figure 9. A reachable marking is then a marking reached through the firing of a transition sequence from the initial one. In Deterministic and Stochastic Petri Nets DSPNs , common metrics are the probabilities associated to the reachable markings, which can be either time-dependent transient metrics or time-independent steady-state metrics.
DSPNs are characterized by two types of transitions: immediate and timed. Once enabled, an immediate transition fires immediately while a timed transition has an associated firing delay, which can be a constant value deterministic or a mean value of the negative exponential distribution stochastic. Place and transition labels have been introduced to enable the net composition. For the modelling step, several tools support UML design.
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Author information Article notes Copyright and License information Disclaimer. Received May 25; Accepted Jun This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This article has been cited by other articles in PMC. Abstract Assessment of software nonfunctional properties NFP is an important problem in software development.
Introduction Model-driven development [ 1 ] MDD is an evolutionary step that changes the focus of software development from code to models, with the purpose of automating the code generation from models.
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Open in a separate window. Figure 1. Integrating dependability modeling and analysis in a UML-based software development. The design model illustrates the following: how dependability techniques can be modeled with UML behavioral diagrams and DAM annotations introduce dependability parameters; how DAM leverages this design for dependability analysis purposes.
Figure 2. In order to define the system fault assumptions, a software engineer has to consider the following main issues: which components can be affected by faults and in which states, the maximum number of faults that can concurrently affect the system components, the complete fault characterization, such as the fault occurrence rate. State Machines Specification Our UML-SMs specification illustrates how the engineer can model specific dependability techniques while describing the system normal behavior.
GUARDS: A Generic Upgradable Architecture for Real-Time Dependable Systems
DAM Specification The fault masking specification i. States Figure 3 a shows the transformation of a simple state with an entry action and a do-activity. Figure 3. Timing Specs The doActivities annotated with corresponding processing demands, are translated into timed transitions, as in Figure 3 a , and the value field of the hostDemand tagged-value is mapped to the input time parameter of the corresponding DSPN transition. Figure 4. Composition of the DSPN subnets over interface places. Figure 5. Analysis and Assessment Results Let us consider the following question: could the system carry out its computations in the presence of faults due, for example, to software bugs or nodes failures?
Figure 6. Figure 7. Related Work Paper [ 18 ] extensively surveys works on dependability modeling and analysis of software systems specified with UML.
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Conclusion A standard specification framework is yet needed for dependability assessment of UML-based specifications. Appendix A. Figure 8. Introduction to Petri Nets A Petri net PN —shown in Figure 9 —is a bipartite graph, in which the vertices can be either transitions or places. Figure 9. References 1.
Selic B. The pragmatics of model-driven development. IEEE Software.
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