A set is a structure that allows access to all records of a data set in some logical sequence.

The set contains one entry for each record in the data set. Each set entry is an index that locates a data set record. If key items are specified for the set, records in the data set are accessed based upon these keys; otherwise, the records are accessed sequentially.

Multiple sets can be declared for a single data set, thereby enabling the data in a data set to be accessed in several different sequences.