When the BASED keyword is specified for a data structure or standalone field, a basing pointer is created using the name specified as the keyword parameter. This basing pointer holds the address (storage location) of the based data structure or standalone field being defined. In other words, the name specified in positions 7-21 is used to refer to the data stored at the location contained in the basing pointer.
If an array is defined as a based standalone field it must be a run-time array.
If a based field is defined within a subprocedure, then both the field and the basing pointer are local.