I use ISO 8601 to represent dates & durations and all is OK. But now I need to represent relative dates and durations like:
In fact I need to have a syntax for it, I prefer a standard one. I don't need code (I yet have all the code) but a syntax to store relatives date or durations just like ISO 8601 use "P1Y2M10DT2H30M" for a duration.
Thanks...
Not a standard, but a convention used by FogBugz and Jira (both bugtrackers) is to enter durations in simple terms like 2d for 2 days, 3w for 3 weeks, 1m for 1 month, etc.
The convention could be extended for dates and periods relative to some other date (usually the current date I presume).
To specifiy periods instead of just dates, you could double up the letters:
To specify a period between two specific relative dates:
Parsing could become an interesting business...
If I understand what you mean correctly, you wish to have a way to say DateTime.NextSunday? If that's the case, as far as I know there isn't a standard you can use for that.
The two examples you gave above are specific examples of a date you need. You would still express the date time using the ISO standard, you just have to prgrammatically define what each means.
How I would do this is in my UI, I'd have a button called "Next Week". Here in Canada, the first day of the week is Sunday, but that's not the same for everyone. Thus I'd write my code like this (c# is my language of choice):
DateTime today = DateTime.Now;
int daysToSunday = (DayOfWeek.Sunday - DateTime.Now.DayOfWeek) + 7;
DateTime weekStart = today.Date.AddDays(daysToSunday);
Note, I didn't test this, just a quick write-up.
Moral though, is that for a concept of time like those you've stated above, you need to code a solution to arrive at those dates.
In the Java world Joda Time supports this kind of operation with respect to your locale meaning it adjusts automatically for the small cultural differences if you need it to.
For example you could create a DateTime which is absolute (today) and add it a relative period (today.plusDays(7) to add a week for example). It also supports many ways to convey this concept of relative duration depending on your use case.
If you do not use Java, I still suggest you look at it to see what to look for in a good calendar management library for your own environment or give you inspiration on making your own.
Careful here though if you decide to go custom, time and dates are simple concepts but only on the surface. There is a lot of adjustments that need to be done to the time in the background to keep it's absolute (a second is a second) and relative (at noon the sun should be at it's zenith) natures in check. Creating your own implementation is simple until you get errors when dealing with such things, combine the microsecond or more precision of computers and their absolute autistic trait they are quite inept when times come to deal with fuzzy concepts that we humans take for granted.
Hope this helped !
