Earning Points. Starwood's Preferred Guest program is fairly straightforward: the more nights you spend at participating hotels, the faster you'll earn a free night.
The mapper output (intermediate data) is stored on the Local file system (NOT HDFS) of each individual mapper nodes. This is typically a temporary directory location which can be setup in config by the hadoop administrator. The intermediate data is cleaned up after the Hadoop Job completes.
The MapReduce framework is inspired by the Map and Reduce functions used in functional programming. Computational processing occurs on data stored in a file system or within a database, which takes a set of input key values and produces a set of output key values.