An Ode To ISO 8601

Last week I posted about ISO 8601 dates on Twitter/X , so I wanted to update those no longer on Twitter/X.

If you’re a developer like me you probably know about the basics of ISO 8601, but you might be surprised by ISO 8601 versatility and expressibility. Let’s dive into the world of ISO 8601 using October 14, 2024, as our playground:

Core Date and Time Representations

• 2024-10-14: This is the basic date format. Simple, straightforward.
• 20241014: A compact form, no separators, useful for file naming or data exchange where space is at a premium.
• 2024-10-14T12:30:00: Here, we add time. ‘T’ separates date from time, making the format clear and unambiguous.
• 2024-10-14T12:30:00.789: Including milliseconds when precision matters.
• 2024-10-14T12:30:00Z: ‘Z’ denotes UTC time, critical for global coordination.
• 2024-10-14T06:30:00-06:00: Time with an offset from UTC, essential for understanding local times worldwide.

Week and Ordinal Date Formats

• 2024-W42: Denotes the 42nd week of 2024. Useful in project management or scheduling where weeks are the primary unit.
• 2024-W42-1: This specifies Monday of week 42. Remember, week days start at 1 for Monday in ISO 8601.
• 2024-288: Represents the 288th day of 2024, which can be handy for daily logs or event tracking.

Duration and Periods

• P1Y2M3DT4H5M6S: This string describes a duration of 1 year, 2 months, 3 days, 4 hours, 5 minutes, and 6 seconds. ISO 8601 uses ‘P’ for period at the start.
• PT1.5H: A simpler form to denote 1.5 hours, showing you don’t always need to specify every component.

Handling Uncertainty

• 2024-06-05?: Indicates a questionable date.
• 2024-06-05~: Suggests an approximate date.
• 2024-06%: Implies the event occurred sometime in June 2024.
• 2024-06~-05: You’re certain about the day, less so about the month.

Recurring Intervals

• R29/2024-10-01T14:00:00Z/PT8H: This means repeat 29 times, starting at the given UTC time, every 8 hours. Ideal for scheduling recurring events or reminders.

By understanding these formats, you enhance your ability to handle date and time in a manner that’s both precise and universally understood. Remember, ISO 8601 isn’t merely a standard; it’s a tool to ensure clarity and consistency across different systems and cultures. So, let’s use it to make our code not just functional, but exemplary in its temporal accuracy.

Below is some fun I had with Claude (an LLM) to generate an ode to ISO 8601 that demonstrates the formats above.

Oh, ISO 8601, you chronological delight, Bringing order to dates, both day and night. From basic to extended, you cover it all, Let’s dive into your formats, both big and small!

A Date to Remember

2024-09-04, oh how you shine!
Year, month, and day, all in a line.
No confusion here, it’s crystal clear,
September 4th, 2024, my dear.

But wait! You’re so flexible,
Your basic format is quite collectible:
20240904, all smooshed together,
For when hyphens are light as a feather.

Time Waits for No One

But dates alone? That’s just the start,
Let’s add some time, and make it smart:
2024-09-04T15:30:00
Hour, minute, second - precision’s your vow!

For those who like their time more compact,
153000 is equally exact.
But what about fractions, you might ask?
2024-09-04T15:30:00.5 - decimal seconds, what a task!

Zoning Out

“But wait,” you cry, “What time zone is that?”
ISO 8601 says, “I’ve got you, stat!”
2024-09-04T15:30:00+02:00
Two hours ahead of UTC, now you know!

For UTC itself, just use a Z,
2024-09-04T13:30:00Z
“Zulu time,” they call it, how fancy!
No offset needed, it’s UTC, you see?

Weeks and Ordinal Dates

But some folks like to count their weeks,
ISO 8601 has what everyone seeks:
2024-W36-3 is our special day,
The 3rd day of the 36th week, hooray!

Ordinal dates, now there’s a treat,
2024-248 is oh so sweet.
The 248th day of the year, my friend,
A format that’ll make your head spin!

Intervals

Need to express a range of time?
ISO 8601 does it with rhyme:
2024-09-04T13:30:00Z/2024-09-05T02:15:00Z
From start to finish, it’s all in the zone.

Duration’s another trick up its sleeve,
P1Y2M3DT4H5M6S, would you believe?
One year, two months, three days, they say,
Plus four hours, five minutes, six seconds - okay!

For the Developers Among Us

Now, for you coders with curious minds,
Here are some formats to tickle your rinds:

Repeating Intervals

R5/2024-09-04T09:00:00Z/PT2H30M
Repeat five times, starting today at nine,
Every two hours and thirty minutes, feeling fine!

Uncertain or Approximate Dates

2024-09-04? - Maybe it’s this day
2024-09~04 - September-ish, we’d say
2024-09-04% - This date’s approximate, okay?

Significant Digits

2024-09-04S3 - Year to day, that’s all we know
2024-09-04S6 - Precise to the minute, oh how it shows!

Date Accuracy

2024-09-04:02 - Give or take 2 days, my friend
2024-09-04:05:01 - 5 days and 1 hour, at either end

Weeks and Ordinal Dates: The Road Less Traveled

But some folks like to count their weeks,
ISO 8601 has what everyone seeks:
2024-W36 is our current week,
A format that’s both strong and sleek.

Want to get more specific? No need to be meek,
2024-W36-3 is our special day of the week.
The 3rd day of the 36th week, hooray!
Wednesday, September 4th, hip-hip hurray!

For those who love their weeks concise,
2024W36 and 2024W363 are also nice.
No hyphens here, just numbers tight,
For when every character’s a delight.

Remember, the week starts on a Monday,
ISO says it’s the only way!
So 2024-W36-1 was September 2nd, you see?
And 2024-W36-7 is the Sunday, whoopee!

Ordinal dates, now there’s a treat,
2024-248 is oh so sweet.
The 248th day of the year, my friend,
A format that’ll make your head spin!

Day of the Year: Counting Up the Calendar

Now let’s talk ordinal dates, a numerical delight,
Counting days of the year, from New Year’s night.
2024-248 is our current day so fine,
The 248th day of 2024, right on time!

In this compact format, so neat and trim,
We see the year, then days - no need to skim.
No months to fuss with, just a simple count,
From 001 to 365 (or 366), the days we surmount.

For 2024, a leap year of note,
We’ve got an extra day to promote:
2024-366 will be our grand finale,
December 31st, ending the year merrily.

Some more examples, to make it clear:
2024-001 is January 1st, Happy New Year!
2024-032 is February 1st, don’t you know,
And 2024-060 is February 29th, leap day’s show!

For non-leap years, adjust your view,
2025-365 will be the year-end cue.
It’s simple, it’s clear, it’s ordinal perfection,
ISO 8601’s day-counting section!

This format’s handy for many a reason,
Calculating days or tracking the season.
In programming or data, it’s often preferred,
For date math that’s simple, no errors incurred.

So next time you’re asked, “What day is today?”
You can say, “It’s 2024-248!” in a nonchalant way.
Watch as they ponder, their brows slightly furrowed,
Then explain ISO’s system, leave them thoroughly wowed!

In Conclusion: A Toast to ISO 8601

So here’s to you, ISO 8601,
A standard that makes our lives great!
From basic dates to complex time,
You handle it all, so sublime.

You bring order to the chaos of dates,
Across borders and timezones, you’re first-rate.
No more MM/DD or DD/MM confusion,
With you, there’s only one conclusion:

YYYY-MM-DD is the way to go,
For dates that everyone can know.
So let’s raise a glass to this standard so fine,
ISO 8601, you’re simply divine!