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4.2.8.2 Access Modes
Sequential-Access Mode
Allows reading and writing records of a file in a serial manner; the order of reference is implicitly determined by the position of a record in the file.
Random-Access Mode
Allows reading and writing records in a programmer-specified manner; the control of successive references to the file is expressed by specifically defined keys supplied by the user.
Dynamic-Access Mode
Allows the specific input-output statement to determine the access mode. Therefore, records can be processed sequentially and/or randomly.
For EXTERNAL files, every file control entry in the run unit that is associated with that external file must specify the same access mode. In addition, for relative file entries, data-name-4 must reference an external data item and the RELATIVE KEY phrase in each associated file control entry must reference that same external data item in each case.

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