A navigation model describes the possible sequences of web pages a user can visit, and a request routing model describes how server side components handle each request. Earlier we developed formal models and analysis operations for such models. While each is useful independently, their utility is greatly improved by relating the models, which is the contribution described in this paper. We describe mappings between the models, and show that the mappings preserve navigation behavior and are bijective, thus supporting traceability and allowing the models to be used in round-trip engineering. With these mappings built into our Model Helper tool, it is now possible to automatically determine whether a Request Routing model conforms to the navigation design, and to automatically generate a Request Routing model from a navigation model. Finally, we describe one of a number of case studies where we used Model Helper in a round-trip engineering scenario.