EDTF (Extended Date/Time Format) Documentation

Overview

The Extended Date/Time Format (EDTF) is used to represent dates that are uncertain, approximate, partial, or expressed as ranges. This database uses EDTF Level 1 as specified by the Library of Congress: https://www.loc.gov/standards/datetime/

EDTF Patterns

Complete Dates

1985-06-15    # June 15, 1985
1985-06       # June 1985 (day unknown)
1985          # Year 1985 (month and day unknown)

Uncertain Dates (?)

Use ? when the date is uncertain but believed to be correct:

1985?         # Possibly 1985
1985-06?      # Possibly June 1985
1985-06-15?   # Possibly June 15, 1985

Approximate Dates (~)

Use ~ when the date is approximate:

1985~         # Approximately 1985
1985-06~      # Approximately June 1985

Uncertain AND Approximate (%)

Use % when a date is both uncertain and approximate:

1985%         # Approximately and uncertainly 1985

Date Ranges (/)

Use / to indicate a range from one date to another:

1985/1990              # Period from 1985 to 1990
1985-06/1985-08        # From June 1985 to August 1985
1985/1990~             # From 1985 to approximately 1990
1985?/1990?            # From possibly 1985 to possibly 1990

Open Ranges

1985/..       # From 1985 onwards (open end)
../1990       # Until 1990 (open start)

Decades and Centuries

198X          # 1980s (any year in the 1980s)
19XX          # 20th century (any year 1900-1999)

Note: This is EDTF Level 2; use with caution and document clearly.

Comparison with ISO 8601

Feature ISO 8601 EDTF
Exact dates ✅ 1985-06-15 ✅ 1985-06-15
Partial dates ❌ ✅ 1985-06, 1985
Uncertainty ❌ ✅ 1985?
Approximation ❌ ✅ 1985~
Ranges ✅ 1985-06-15/1985-08-20 ✅ 1985/1987
Decades ❌ ✅ 198X (Level 2)

EDTF extends ISO 8601 with features needed for cultural heritage and historical research.

References

  • EDTF Specification: https://www.loc.gov/standards/datetime/
  • EDTF on Wikipedia: https://en.wikipedia.org/wiki/Extended_Date_Time_Format
  • Python EDTF Library: https://pypi.org/project/edtf/
  • Use in Digital Humanities: See Dublin Core and Europeana implementations

Glossary

  • Uncertain (?): The date is questionable but believed to be correct
  • Approximate (~): The date is not exact but close
  • Both (%%): Combination of uncertain and approximate
  • Range (/): Period from start date to end date
  • Open range (..): One end of the range is unknown or ongoing
  • Level 1: Core EDTF features (recommended for this project)
  • Level 2: Extended features (use sparingly and document)
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