A hierarchical modeling framework for the dependability evaluation of Internet-based applications is presented and illustrated on a travel agency example. Modeling is carried out considering four levels, namely: user, function, service and resource levels. The first level describes how the users invoke the application and the three remaining levels detail how the user requests are handled by the application at distinct abstraction layers. The user perceived availability measure considered in this paper takes into account the combined impact of performance-related failures and traditional software and hardware failures. For illustration purposes, several sensitivity analysis results are presented to show the impact on this measure of various assumptions concerning, e.g. the users operational profile, the travel agency architecture and the fault coverage.
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