Who is responsible for deleting the files on file system if BP storage is set to file system  

Answer

Sterling Integrator version 5.0

When the document store for a BP is "file system", all documents created by the BP will be written to the file system.
The filename on disc contains the BP id at the end of the filename.
Status reports will also be stored in disc.
Files with -1 at the end of the filename relate to mailboxes.

If no further reference to the documents exists, the documents will be purged during backup/purge of the business process.

If the BP contains these actions, the life span is different to the BP life span:-
- Call of a child processes with a longer life span and the child process works with the document.
  The document will be purged/archived during purge/archive of child process.
- Human Interaction Event Server with Operation=ADD will be flagged with an expiration date of 10 years in the future. 
  This is to prevent the document from being purged or archived before the required action is performed. 
   Once this event is deleted with the Human Interaction Event Server with Operation=DELETE, the document expiration date will be changed to the current time making it eligible for archiving or purging.
- Envelope/DeEnveloping actions get a longer life span for acknowledgment reason.
  The default life span can be changed by editing the document.lifespan property in the enveloping.properties file.
  The document life span of the outbound document is automatically reset to zero after the acknowledgement for the document is received or if the user manually accepts the acknowledgement.
- mailbox actions will lead to a life span of 10 years, so that a download is possible.
  After deletion in mailbox the life span will be recalculated.