This chapter explored the first simple pattern that leverages and works around some of the Web Service details. Clients create event monitors when they have little or no control over a server-side component, such as an independently created Web Service, and need to be aware of state changes in the server-side component. The event monitor has many limitations, detailed in this chapter, with its primary strength being a client's ability to build the event monitor after the fact.
The sample code for the event monitor builds on top of the business process created in the previous two chapters. Business processes are often good targets for event monitors because they are long running and must run asynchronously.
Although event monitors may be necessary in programming, a better strategy is to build up adequate event interfaces before you deploy Web Services for client usage. Imagine having 100 independent clients polling your Web Service every second, or, worse , imagine 10,000 clients polling your Web Service every second. By providing appropriate event mechanisms, you control when and how often event delivery should occur.