How does an Hadoop application look like or their basic components?

Minimally an Hadoop application would have following components.
 Input location of data
 Output location of processed data.
 A map task.
 A reduced task.
 Job configuration
The Hadoop job client then submits the job (jar/executable etc.) and configuration to the JobTracker which then assumes the responsibility of distributing the software/configuration to the slaves, scheduling tasks and