Case files are distinct events tracked by some organization. They have a start date and end date, an identifying number, and assigned users and groups. Case files include tasks, folders, and documents.
For Freedom of Information Act (FOIA) agencies, a case (also known as a request) starts when a citizen requests information, and ends after the request is resolved. The users are analysts and supervisors. The tasks include record searches, redaction of records, and billing. The documents include the records to be delivered to the citizen.
For law enforcement agencies, a case starts when a crime is reported, and ends after either a criminal prosecution, or determination the crime can't be solved. The users are detectives, investigators, evidence specialists, and so on. The tasks include leads and witness interview requests. The documents include investigation reports, interview transcripts.
Complaints are much like case files. Complaints allow the customer to pursue a report without opening an official case file. This allows some work to be done, without incurring all the compliance requirements of a full case file. Complaints are converted into a case file if the organization decides the complaint is a substantial matter and should be treated as a full case file. Complaints may also be referred to other organizations (if the matter is real, but should be handled by some other organization), or be closed with no further action (for false alarms or trivial matters).
Document repositories are plain old folders, much like a network shared drive. The folders have no start and end date, like case files and complaints have. They have no compliance requirements, like case files and complaints have. Document repositories allow customers to track libraries such as procedure manuals, historical case files, and personal documents.