The outside-in approach to decomposing an application is an example of one practical way to identify types of concurrent tasks that are dependent on or interact with I/O devices. The mobile handset example expands a high-level context diagram to determine some of the obvious tasks required to handle certain events or actions. Further refinement of this diagram would yield additional tasks. More formalized ways of identifying concurrency exist, however. Many guidelines are provided in this section to help the reader identify concurrency in an application. First, let's introduce a couple of concepts that are important to understanding concurrency.