Databases are essentially large repositories of data. Since the mid-1980s up to the mid-1990s, considerable effort has been paid to incorporate reactive behavior to the data management facilities available. Reactive behavior is characterized by variants of the event–condition–action model. Applications areas include checking for integrity constraints, system alerts, materialized view maintenance (especially useful in data warehousing), replication of data for audit purposes, data sampling, workflow processing, implementation of business rules, scheduling, and many others. Practically all products offered today in the database marketplace support complex reactive behavior on the client side. Nevertheless, the reactive behavior supported by those products on the server side is poor. Recently, the topic has regained attention because of the inherent reactive nature demanded in Web applications and the necessity of migrating many of the functionalities of browsers to active Web servers (Bonifati, Braga, Campi, & Ceri, 2002).