Surrogate key is a replacement for the natural prime key. It is a unique identification for each row in the table. It is very beneficial because the natural primary key can change which eventually makes update more difficult. They are always used in form of a digit or integer.
Option for incremental aggregation is enabled whenever a session is created for a mapping aggregate. Power center performs incremental aggregation through the mapping and historical cache data to perform new aggregation calculations incrementally.
During session runs, the files created are namely Errors log, Bad file, Workflow low and session log.