A model and a language for the description of data-intensive Web applications and a methodology for their development are proposed. The model and the language are extensions of ADM and Penelope, respectively, the model and language defined in the Araneus project. ADM and Penelope were originally developed for “read-only” sites, whereas here, behavioral aspects are introduced. All operations are associated with links or buttons in pages, as users request actions by selecting them, and actions can be basic updates on a database (or combinations thereof) or calls to external modules, defined only by means of interfaces. The management of user privileges is also taken into account.