||The web is more and more used as a platform for full-fledged, increasingly complex applications, where a huge amount of change-intensive data is managed by underlying database systems. From a software engineering point of view, the development of web applications requires proper modeling methods in order to ensure architectural soundness and maintainability. Existing modeling methods for web applications, however, fall short on considering a major requirement posed on today's web applications, namely customization. Web applications should be customizable with respect to various context factors comprising different user preferences, device capabilities and locations in mobile scenarios, to mention just a few. The goal of this paper is twofold. First, a framework of requirements, covering the design space of customizable web applications is suggested. Second, on the basis of this framework, existing approaches for developing customizable web applications are surveyed and general shortcomings are identified pointing the way to next-generation modeling methods.