Web 2.0 Architectures

Consistent Object and Event Models

Our Web 2.0 Reference Architecture leaves some items, such as consistent object and event models, outside of the tiers themselves. These items relate to several tiers of the reference model. For example, if a developer wishes to develop an application that listens for changes to the state of an object and catches them as events, the entire architecture must have a consistent model for objects and events, or at least a model for making them consistent eventually.^[66] These models may vary slightly if the developers are using several technologies within their projects, and it is important for architects to understand and be able to account for the differences. Consider an Adobe Flex frontend (client-tier) application that is coupled with a .NET backend (server tier). If the Flex client needs to capture events, the model of how events are generated and detected and how messages are dispatched has to be consistent throughout the entire application.

Some Web 2.0 patterns, such as the Mashup and Synchronized Web patterns (described in Chapter 7), demand a consistent model for both objects and events. Those building composite applications might have to deal with events occurring on objects residing in several remote domains and different environments. SOA makes this somewhat easier by providing a clearly defined interface to the objects; however, the high-level models need to be aligned.

Over the past decade, this has become easier. The W3C recognized the ...