Working With Dates at Century Boundaries

AppleScript's support for dates is based on the same operating system utilities other Macintosh applications use. Mac OS date and time utilities have correctly handled issues related to the year 2000 since the introduction of the Macintosh. The original date and time utilities, introduced with the Macintosh 128K in 1984, use a 32-bit value to store seconds, starting at 12:00:00 a.m., January 1, 1904 and extending to 6:28:15 a.m. on February 6, 2040.

More recent date and time utilities use a 64-bit signed value that can represent dates from 30081 B.C. to 29940 A.D. However, AppleScript currently will not handle dates before 1/1/1000 or after 12/31/9999. For more information on Mac OS date and time utilities, see Inside Macintosh: Operating System Utilities. available at the Apple Developer website:

www.apple.com/developer

Figure 6-1 Two-digit dates at century boundaries

Two-digit dates near the year 2000, or any century boundary, may still represent a problem if your script accepts two-digit dates as text from applications or users. Whenever your script calls on AppleScript to convert a two-digit date to a Date value, AppleScript converts the text representation to a full date for internal storage, following the rules illustrated in Figure 6-1 and summarized here:

If the current year is late in any century (years 91 to 99)

a date with a year value from 11 to 99 is in the current century (in 1999, for example, 11 = 1911 and 99 = 1999)
a date with a year value from 00 to 10 is in the next century (in 1999, for example, 03 = 2003)

If the current year is early in any century (years 00 to 10)

a date with a year value from 00 to 90 is in the current century (in 2000, for example, 00 = 2000, 45 = 2045, and 90 = 2090)
a date with a year value from 90 to 99 is in the previous century (in 2000, for example, 99 = 1999)

If the current year is in the middle of any century (years 11 to 90)

a date with any value for year value, from 00 to 99, is in the current century (in 2011, for example, 00 = 2000, 45 = 2045 and 99 = 2099)

So a script that uses nearby dates, such as for office scheduling or other near-term planning, can use two-digit dates with some degree of safety. However, a script that does long-term date calculations, such as for genealogy or mortgages, should require four-digit dates.