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A time interval is the intervening time between two time points. The amount of intervening time is expressed by a duration (as described in the previous section). The two time points (start and end) are expressed by either a combined date and time representation or just a date representation. There are four ways to express a time interval:
Federal regulations for shelf life dates on perishable goods mandate a year/month/day format, but allow the month to be written in full, in both official languages, or with a set of standardized two-letter bilingual codes such as 2019 AL 09 or 19 AL 09. CAN/CSA-Z234.4-89 (R2007) [36] Cape Verde: No: Yes: No Cayman Islands: No: Yes: Yes
In communications messages, a date-time group (DTG) is a set of characters, usually in a prescribed format, used to express the year, the month, the day of the month, the hour of the day, the minute of the hour, and the time zone, if different from Coordinated Universal Time (UTC).
While the native APIs of OpenVMS can support timestamps up to 31 July 31086, [28] the C runtime library (CRTL) uses 32-bit integers for time_t. [29] As part of Y2K compliance work that was carried out in 1998, the CRTL was modified to use unsigned 32-bit integers to represent time; extending the range of time_t up to 7 February 2106.
These timestamps ensure that transactions affect each object in the same sequence of their respective timestamps. Thus, given two operations that affect the same object from different transactions, the operation of the transaction with the earlier timestamp must execute before the operation of the transaction with the later timestamp.
Timestamps do not have to be based on some absolute notion of time, however. They can have any epoch, can be relative to any arbitrary time, such as the power-on time of a system, or to some arbitrary time in the past. A distinction is sometimes made between the terms datestamp, timestamp and date-timestamp:
When dealing with periods that do not encompass a UTC leap second, the difference between two Unix time numbers is equal to the duration in seconds of the period between the corresponding points in time. This is a common computational technique. However, where leap seconds occur, such calculations give the wrong answer.
The 64-bit timestamps used by NTP consist of a 32-bit part for seconds and a 32-bit part for fractional second, giving NTP a time scale that rolls over every 2 32 seconds (136 years) and a theoretical resolution of 2 −32 second (233 picoseconds). NTP uses an epoch of 1 January 1900.