Question-11: What Mapper does?

Answer: Mapper are the individual task that transform input records into intermediate records. And then transformed intermediate records do not need to be of the same type as the input records. A given input pair may map to zero or many output pairs. 

Question-12:  What is the InputSplit in map reduce software?

Answer:An InputSplit is a logical representation of a unit or a chunk of input work for a map task. For example, a filename and a byte range within that file to process or a collection of rows in a text file.

Question-13: What is the InputFormat?

Answer: The InputFormat is responsible for enumerate or itemise the InputSplits, and producing a RecordReader which will turn those logical work units into actual physical input records.

Question-14: Where do you specify the Mapper Implementation?

Answer: Generally, mapper implementation is specified in the Job itself.

Question-15: How Mapper is instantiated in a running job?

Answer: The Mapper itself is instantiated in the running job, and will be passed a MapContext object which it can use to configure itself.