ange partners may not be able to accept dates in expanded format. Date Windowing Two-digit year values can be windowed, by assuming that the year must fall within a 100-year range. This method is essentially how abbreviated dates work right now -- the 100-year period is assumed to be from 1900 to 1999, inclusively. If the 100-year range assumption is from 1950 to 2049, and correct instructions are written in the software, the software will perform date processing correctly until 2050. The date window can be set to any 100-year period, or can be interpreted according to the current year (e.g. from 10 years before this year to 89 years after this year). Date windowing requires no changes to data storage, no conversion of old data, and no changes to screens or reports. Date windowing has a number of disadvantages, however. The code to perform the interpretation of dates must be written very carefully, keeping in mind the varying requirements of all of the applications that may use or interact with the dates. Within a single application, an employee birth date may require a window range entirely in the past, while a forecasting function will require a range entirely in the future. All users of the application, and any other application that may share the data, must be cognizant of the assumptions made in every circumstance. At some point, most windowing techniques will require further modifications to continue to function. Windowing is inherently ambiguous, and should not be used in applications requiring the exchange of data across systems. Date Setback There are two types of date setback techniques, one requiring the manipulation of data, and the other involving the system clock itself. The year data can be set back by 28 years (or 56; the calendar repeats itself every 28 years), making "98" appear to be "70" (or "42"). This approach is by far the riskiest, as it involves changes to both code and data, requires alteration of...
