ISO 8601
Overview
ISO 8601 is an international standard covering the exchange of date- and time-related data. It was issued by the International Organization for Standardization (ISO) and was first published in 1988. The purpose of this standard is to provide an unambiguous and well-defined method of representing dates and times, so as to avoid misinterpretation of numeric representations of dates and times, particularly when data are transferred between countries with different conventions for writing numeric dates and times.
Structure of the Standard
The ISO 8601 standard is structured into various sections, each dealing with a different aspect of date and time representation. These include calendar dates, ordinal dates, week dates, local time, time of day, time intervals, recurring time intervals, and the representation of dates and times in information interchange.
Calendar Dates
In ISO 8601, the calendar date is represented in a specific format: YYYY-MM-DD. This is a departure from other date formats that vary from country to country. The standard stipulates that the year must be represented by four digits, the month by two digits (01 for January to 12 for December), and the day by two digits (01 to 31).
Ordinal Dates
Ordinal dates are a particular feature of ISO 8601. They are represented as the year followed by the day of the year, running from 001 to 366. This format is useful in certain applications, particularly where the cyclical nature of the calendar year is important.
Week Dates
ISO 8601 also specifies a system for week dates, where each week is associated with the year in which Thursday occurs. This means that week 01 of a year is the week that includes the first Thursday of that year.
Local Time
The standard allows for local time to be indicated by appending the time zone offset to the time of day. The offset is represented by appending a plus or minus sign, followed by the time difference from Coordinated Universal Time (UTC).
Time of Day
The ISO 8601 standard also covers the representation of time of day. The time is represented as a string of digits, separated by colons, in the format HH:MM:SS. The hours are represented in a 24-hour format.
Time Intervals
ISO 8601 defines several ways to represent time intervals. These can be represented as a start and an end time, as a start time and a duration, or as a duration only.
Recurring Time Intervals
The standard also provides a way to represent recurring time intervals, to specify repeating events.
Usage
ISO 8601 is widely used in many contexts, including computing, data interchange, electronic data interchange (EDI), and more. Its adoption is widespread because it reduces the chance of misinterpretation of dates and times, particularly in international contexts. It is also used in some legal and contractual documents.
Criticism and Limitations
Despite its widespread adoption, ISO 8601 has been subject to some criticism. Some users find the format unfamiliar or confusing, particularly in regions where the date format differs significantly from the ISO standard. Additionally, the standard is limited in that it does not account for certain calendar systems, such as the lunar calendar used in some cultures.