Data Management Skillbuilding Hub

Best Practice: Describe formats for date and time


Best Practices by Data Life Cycle

Describe formats for date and time

Data Life Cycle stage(s): Describe

For date, always include four digit year and use numbers for months. For example, the date format yyyy-mm-dd would appear as 2011-03-15 (March 15, 2011).

If Julian day is used, make sure the year field is also supplied. For example, mmm.yyyy would appear as 122.2011, where mmm is the Julian day.

If the date is not completely known (e.g. day not known) separate the columns into parts that do exist (e.g. separate column for year and month). Don’t introduce a day because the database date format requires it.

For time, use 24-hour notation (13:30 hrs instead of 1:30 p.m. and 04:30 instead of 4:30 a.m.). Report in both local time and Coordinated Universal Time (UTC). Include local time zone in a separate field. As appropriate, both the begin time and end time should be reported in both local and UTC time. Because UTC and local time may be on different days, we suggest that dates be given for each time reported.

Be consistent in date and time formats within one data set.

Description Rationale

The date and time are important pieces of contextual information for observations. A complete description of date and time allows the observation to be used and interpreted properly.

Additional Information

ISO 8601 format date: YYYY-MM-DD time: HH:MM:SS datatime: YYYYMMDDTHHMMSS



Cite this best practice:

DataONE Best Practices Working Group, DataONE  (July 01, 2010) "Best Practice: Describe formats for date and time". Accessed through the Data Management Skillbuilding Hub at on May 24, 2019


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