File processing

A file is a collection of records that can be moved to, or read from, a volume. The user defines the organization of the file as well as the mode and order in which the records are processed.

The organization of a file describes its logical structure. There are sequential, indexed, and relative types of file organization. The file organization which is defined at the time a file is created cannot be changed later on.

A sequential file can only be processed sequentially, i.e. the records are either read or written in the order predetermined by the file. In the case of sequential files on disk storage devices, records may also be updated in place. This requires a READ statement followed immediately by a REWRITE.