UML-Ψ: the UML Performance SImulator

In this paper we describe UML-Ψ, a software performance evaluation tool based on process-oriented simulation. The tool can be used to evaluate performances of software systems which are described at a high level of abstraction. This allows the software modeler to estimate the system performances before actually building it, at the design phase. We consider software specifications as Unified Modeling Language (UML) diagrams annotated according to a subset of the stereotypes and tagged values defined in the UML Performance Profile. UML-Ψ transforms the software model, i.e., the set of UML annotated diagrams, into a performance process-oriented simulation model. Simulation parameters are derived by the software description and the additional information given in the specification. Simulation experiments are carried on by choosing an appropriate condition for the length of the simulation run. The tool collects observations and derives estimates of a set of performance measures. Performance results are interpreted at the software specification level, as they are inserted into the software model as tagged values associated to the relevant UML elements. Further analysis can be applied to the possibly modified software model in order to meet given performance requirements. We illustrate with an example how the UML-Ψ tool can be used.