There are two kinds of keys, recorded keys and source keys. A recorded key is a character string that immediately precedes each record in the data set to identify that record; its length cannot exceed 255 characters. A source key is the character value of the expression that appears in the KEY or KEYFROM option of a data transmission statement to identify the record to which the statement refers. When you access a record in a regional data set, the source key gives a region number, and can also give a recorded key.
Unlike the keys for indexed data sets, recorded keys in a regional data set are never embedded within the record.