Constructing performance models of e-commerce systems is expensive to develop and validate. Performance assurance is a methodology that, when applied during the design and development cycle, will greatly increase the chances of immediate user satisfaction in an e-commerce project. System performance validation provides assurance that a system as a whole is likely to meet its quantitative performance goals. It applies performance engineering methods and tools during a system?s development and has to be integrated into the design process from the very beginning through to system deployment. In this paper, we discuss the transformation of Unified Modeling Language (UML) models into software execution models and simulate the performance prediction for an e-commerce application. We exploit the features of UML 2.0. Application of the procedure is illustrated with a case study of e-parking system.