Set Order

The logical order in which new members are linked into a set occurrence follows one of the following user-specified methods:

FIRST- A LIFO (last-in first-out) order. The new record is positioned immediately after the owner record.
LAST- A FIFO (first-in first-out) order. The new record is positioned immediately before the owner record (that is, after the last existing member record). PRIOR pointers are required.
NEXT- A simple list. The new record is positioned immediately after the current (most recently accessed) record.
PRIOR- A reverse list. The new record is positioned immediately before the current record. PRIOR pointers are required.
SORTED- A sorted list or index. The new record is positioned according to the value of one or more of its elements (called a sort key) relative to the values of the same element(s) in the other member records. Member records can be arranged in ascending or descending order with respect to the designated sort key. For example, if the sort key is employee last name arranged in ascending order, then June Moon will be added after John Done in the set.
Records with duplicate sort key values can be positioned first or last of members with the same values, or they can be disallowed, ensuring that each member in the set has a unique sort key value.

Note: An element that is part of a sort key is also referred to as a sort control item.

The following diagram illustrates the effects of NEXT and PRIOR set order in a chain set. We are positioned on Sandy Shore and add June Moon. If the set order is NEXT, June Moon follows Sandy Shore. In a PRIOR-ordered set, June Moon precedes Sandy Shore.

The following diagram illustrates the effects of FIRST and LAST set order in a chain set. In each case, we add four records to the database: Peter Plum, Sandy Shore, John Done, and June Moon. If the set order is LAST, each new record is added at the end of all current members. The result is a First-In-First-Out (FIFO) ordering of the members, since the first member in the set is the first member added. If the set order is FIRST, each new record is added ahead of all current members, resulting in a Last-In-First-Out (LIFO) ordering of the members.

The following diagram illustrates the effects of SORTED set order and various duplicates options in a chain set. The sort key is the employee's last name. The first set occurrence represents a set whose members are sorted ascending by last name, while the second represents a set sorted descending by last name. The remaining three show the impact of different duplicates options when a second occurrence of June Moon is added to a set whose sort order is ascending.