The justification for choosing this typing scheme is scalability. In other sys- tems, such as one finds for example in the Java Distributed Event Specifica- tion [SunMicrosystems 1998] andCORBANotification Service [ObjectManage- ment Group 1998b], a notification is a value of some named, explicit notification type. This implies a global authority formanaging and verifying the type space, something which is clearly not feasible at an Internet scale. On the other hand, we define a restricted set of attribute types from which to construct (arbitrary) notifications. By having this well-defined set, we can perform efficient routing based on the content of notifications. As we discuss in Section 7, content-based routing has.
