A precise pattern describing a DateStamp which folks often can quickly grok without language barriers. It also sorts the same as a number or string and as a date type in most RDBMS (if zero-padded). Variations include a space or a dash between elements.

Now available in an international standard near you: http://en.wikipedia.org/wiki/ISO_8601

I wish I could remember the Pattern template off the top of my head, but I wanted to get this posted -- ChrisGarrod

	 '''Yyyy''':	  the year CE as a signed integer, ones in this decade have RegularExpression '''201[0-9]''' -- This format is yNk compliant until y10k, if we want y10k compliance, allow any number of digits in this position. 
	  '''Mm''':	  month, using leading zero for most of them.  RegularExpression: '''0[1-9]|1[0-2]'''
	  '''Dd''':	 day of month, always with two digits, if we ignore leap years and the ThirtyDays litany, the RegularExpression is: '''[0-2][1-9]|[123]0|31''' LeapYear will require a more specialized object.

If you want a PointInTime, just add '''.''''''HhMmSs''' to the date.

Julius''''''Caesar ignored the warning: '''Beware The''''''Ides''''''Of''''''March''', and was assassinated on -430315.
Perhaps it was after 10am and before 8pm: -430315.1

''My personal favorite expression of date is a compressed text string with the three letter abbreviation of the month as the middle portion: 2011Apr25. Only one more character, and kinda hard to "misunderestimate" that one, eh?''

* But it doesn't sort correctly alphabetically.

A different Anon replies, for my own use I've started using 2011_04Apr_25; this way the computer has the number for the month for easier sorting and the human (me) gets the 3 letter text for quicker comprehension.  Also, The way the breakdown is described, the titled version should be '''YYYYMMDD''' (uppercase = required, lowercase = ignore if zero). 

Also with '''[0-2][1-9]|[123]0|31''' LeapYear works fine, xxxx0229 is allowed just like xxxx0431.  A more specialized construct is needed if you don't want to ignore the ThirtyDays litany, or block LeapDay on non leap years. And feel free to DeleteIfCooked my regex comment when it doesn't say the opposite of what it means.