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.

ument do when a robot searches through them to extract useful information. Thus, the members of the "Clever" project decide to classify the sites as "pivot-sites" or "reference-sites" of different domains, from a graph representing the links between the different sites [1]. The "pivot-sites" are sites that contain a number of sites pertaining to a certain domain, and the "reference-sites" are sites that contain pertinent information in the same domain and that are pointed to by the "pivot-sites". This information is collected by robots. (b) They act as active sources of information when the links are spontaneously activated by an end-user and when the activation contains in itself some useful information. If, for example, some links are frequently activated in the same order on a given server, we can deduce that the links are indeed "next" links, like the ones you sometimes find at the bottom of web pages. "Adaptive" sites use this type of information. [2,3] (c) They act as implicit