1. Introduction
Date and time formats cause a lot of confusion and interoperability problems on the Internet. This document addresses many of the problems encountered and makes recommendations to improve consistency and interoperability when representing and using date and time in Internet protocols.
This document includes an Internet profile of the ISO 8601 [ISO8601] standard for representation of dates and times using the Gregorian calendar.
There are many ways in which date and time values might appear in Internet protocols: this document focuses on just one common usage, viz. timestamps for Internet protocol events. This limited consideration has the following consequences:
Limitations and Assumptions for Timestamps
o Current Era
All dates and times are assumed to be in the "current era", somewhere between 0000AD and 9999AD.
o Relationship to UTC
All times expressed have a stated relationship (offset) to Coordinated Universal Time (UTC). (This is distinct from some usage in scheduling applications where a local time and location may be known, but the actual relationship to UTC may be dependent on the unknown or unknowable actions of politicians or administrators. The UTC time corresponding to 17:00 on 23rd March 2005 in New York may depend on administrative decisions about daylight savings time. This specification steers well clear of such considerations.)
o Historical Timestamps
Timestamps may represent times that occurred before the introduction of UTC. Such timestamps are relative to Universal Time, using the best available practice at the stated time.
o Representation of Time Points
Date and time expressions represent an instant in time. Descriptions of time periods or intervals are not covered here.
Key Points:
- This specification focuses on timestamps, not time periods or scheduling
- All times must have a defined relationship to UTC
- Supports date range from 0000AD to 9999AD
- Avoids dependency on political decisions regarding local timezones (such as daylight saving time adjustments)