Web engineering can be seen as the application of software engineering in a particular environment -the Web. Its most important aspect is the orientation towards distributed systems and their current technology. Current specification techniques like UML do not cover concurrency, distribution and deployment in a sufficient way. We propose a modeling technique based on high-level Petri nets, called reference nets. They naturally allow for the modeling of processes. Additionally we introduce a

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... ework that covers the other aspects of Web application modeling. Finally we introduce a tool set based on Renew, a tool for reference nets, to support these modeling approach.