Reusing Bytes and The Redefine
Similiar to the Packed Decimal field, the purpose of a Redefine is to conserve bytes on disk. The Redefine in its simplist terms redefines a contiguous group of bytes. Typically, the selection of what definition to use for the given area of bytes is based on a key, which is just another field in the current row.
Take the following figure as an example:
The Redefine Column in this example is simply the contiguous 10 bytes of space in every row at the same position. The Redefine Column will be made up of 1 or more definition collections that will define the groups of bytes within this contiguous space.
In this example, we have two definition collections, one representing Name and Amount Paid fields for a given row and another using the entire space for a single definition of Address.
The definitions can be a regular column representing text and/or numbers and they can also be Packed Decimal fields consisting of Comp-3 and Zoned bytes.