If the record contains a filler item, the filler item can be reduced in size or eliminated altogether, and new data items and group items can be added in the space made available.

The size of the record must not change. Thus, the filler item must be reduced in size or eliminated to produce the proper size area. Filler items are similar to alpha items. Their size is specified in 8‑bit bytes, they are aligned on byte boundaries, and they are initialized to all bits on. Regardless of the position of the filler item declaration, the filler in the record is located after all data items and group items, and before all control items.

Items added to a fixed-format record must be added at the end of the record. Items added to the fixed part of a variable-format record must be added at the end of the fixed part. Items added to the variable part must be added at the end of the variable part.

New items can be required and must not specify a null initial value. If new items are required, a reorganization also is required. If the new items are required and an initial value is not specified or the initial value is null, a data error occurs during the reorganization. All items added to existing records have the initial value of all bits on. This includes Boolean items and field items. All items in newly created records have normal initial values.

Since the filler item starts on an 8‑bit byte boundary, the first newly added item must start on a byte boundary also. If an unused 4‑bit digit precedes the filler, the first new item is not properly byte aligned. In this case, the error message “ITEM ADDED” or “ITEM MISMATCH” results. To avoid this problem, ensure that the first added item is byte aligned. For example, if one of the new items is an alpha item or group item, put it first. Otherwise, the first new item must be inserted in a dummy group item.

If the change of the REQUIRED option for an item does not affect the location of the first REQUIRED option, it can be used with a DASDL update process. For example, assume the original DASDL description looks as follows:

D DATASET
REQUIRED ALL
(D1    NUMBER(6);
 D2    ALPHA(12);
 D3    NUMBER(6);
);
S SET OF D KEY IS D1;

And the DASDL description is changed to the following:

UPDATE;
D DATASET
(D1    NUMBER(6);
 D2    ALPHA(12);
 D3    NUMBER(6);
);
S SET OF D KEY IS D1;

D1 is implicitly required in data set D because it is the key of set S. Since the location of the first required item (D1) did not change, a reorganization is not required.

When an item is made required, the user must ensure that the item has a valid value in every data set record. The Reorganization program terminates with an error if it encounters a required item containing a null value.

Modifying data items that are used in a where condition can force a reorganization of the subset. Also, adding, deleting, or changing data items that are physically located before items used in a where condition can change the offset of the items in the where condition and force a reorganization of the subset.

Occurrences of an item or a group can be increased or decreased. An OCCURS clause can be added or deleted. Data is lost when occurrences are decreased. When occurrences are increased, items or groups in the new data set record with no source in the old data set record are filled with the appropriate initial value.

If the size of an item or an occuring item within the group is changed, then it is possible that the generated reorganization text that is required to move the data from the old field to the new field might exceed the maximum allowable size. If this happens, the DASDL compiler issues the following error:

THIS REORGANIZATION CANNOT BE DONE
LENGTH OF TEXT REQUIRED FOR REORG EXCEEDS THE MAXIMUM

Other methods, such as using the LOADDUMP utility, can be used to accomplish this reorganization.

If a data item is deleted from a data set or from global data, the data item must also be deleted from all remaps which include it.

An error occurs if you add a new item to an existing data set and use the new item as the key for a new set. The error occurs because, by default, all values of the item are initially null. To avoid this error, complete either of the following actions: