By now there seem to be almost as many date compression schemes as there are kinds of Y2K problems. Just selecting a compression format can be a daunting task. There are, however, several criteria you can use to evaluate a compression format and simpify the task of selection. Here are a few of them.
- Human readability. In some applications it may be important for humans to be able to decipher compressed dates with relative ease. Compression formats vary in how badly they garble the information presented to the casual reader.
- Detectability. Some formats have the advantage that their use can be detected by software. In other words, there is no possibility of misreading a compressed date field as a valid, uncompressed, date.
- Intrusiveness. A nonintrusive format in this context is one requiring no changes to legacy date fields containing dates earlier than January 1, 2000.
Detectability and intrusiveness are closely related properties. If a compressed format is detectable it can be combined with MMDDYY to form a nonintrusive format. The new nonintrusive format is one that uses MMDDYY for all dates before January 1, 2000 and uses the compressed format for all other dates.
- Range of valid dates. Compression schemes vary in how much time they can "buy" an application before it is fixed correctly. (Windowing, which is not a compression scheme, can add at most 100 years to the life of a program.)
- Simplicity. All other things being equal, the simpler compression scheme is likely to be the better one.
Table 1 shows how the compression schemes presented in this article stack up against the above criteria. — mb o