A name can be made unique if it exists within a hierarchy of names, and the name can be identified by specifying one or more higher-level names in the hierarchy. The higher-level names are called qualifiers, and the process by which such names are made unique is called qualification.
Qualification is specified by placing one or more phrases after a user-specified name, with each phrase made up of the word IN or OF followed by a qualifier. (IN and OF are logically equivalent.)
References to Data Division Names - Format 1 .-------------------------. V | >>-+-data-name-1----+----+---------------------+-+--------------> '-condition-name-' '-+-IN-+--data-name-2-' '-OF-' >--+---------------------+------------------------------------->< '-+-IN-+--file-name-1-' '-OF-'
References to Data Division Names - Format 2 >>-LINAGE-COUNTER--+---------------------+--------------------->< '-+-IN-+--file-name-2-' '-OF-'
In any hierarchy, the data name associated with the highest level must be unique, and cannot be qualified.