What is EDTF?

Extended Date/Time Format (EDTF) is a standardized format for representing dates and times that are uncertain, approximate, or otherwise complex. It was developed by the Library of Congress and is based on ISO 8601-2.

The Problem

Traditional date formats like ISO 8601 work well for precise, known dates:

1985-04-12  (April 12, 1985)

But what about dates that are:

• Uncertain: "This artifact is possibly from 1984"
• Approximate: "This event happened around 1950"
• Partially unknown: "This occurred sometime in the 1990s"
• Ranges: "Active between 1940 and 1945"

These scenarios are common in:

• Museums and cultural heritage institutions
• Historical research and archives
• Genealogy and family history
• Academic databases
• Digital humanities projects

The Solution

EDTF extends ISO 8601 to handle these complex date scenarios:

'1984?'           // Uncertain: possibly 1984
'1950~'           // Approximate: circa 1950
'199X'            // Unspecified: sometime in the 1990s
'1940/1945'       // Interval: from 1940 to 1945
'2001-21'         // Season: Spring 2001
'[1667,1668]'     // Set: one of these years

Conformance Levels

EDTF defines three conformance levels:

Level 0: ISO 8601 Profile

Basic date and time representations:

1985-04-12                Complete date
1985-04                   Year and month
1985                      Year only
1964/2008                 Interval
1985-04-12T23:20:30Z      Date and time with timezone

Level 1: Extensions

Adds uncertainty, approximation, and basic extensions:

1984?                     Uncertain
2004-06~                  Approximate
2004-06-11%               Uncertain and approximate
201X                      Unspecified digit
Y170000002                Extended year
2001-21                   Season (Spring)
../1985-04-12             Open-ended interval

Level 2: Advanced Features

Complex expressions for specialized use:

Y-17E7                    Exponential year
1950S2                    Significant digits
[1667,1668,1670]          Set (one of)
{1667,1668,1670}          List (all of)
?2004-06-~11              Partial qualification
2001-33                   Quarter (Q1)

Real-World Examples

Museum Cataloging

import { parse } from '@edtf-ts/core';

// Artifact with uncertain date
const pottery = parse('156X-12-25');
// "December 25, sometime in the 1560s"

// Painting from approximate period
const painting = parse('1887~');
// "circa 1887"

Historical Research

// Battle with known month but uncertain day
const battle = parse('1777-09-XX?');
// "Some day in September 1777 (uncertain)"

// Historical period
const renaissance = parse('1400/1600');
// Interval from 1400 to 1600

Genealogy

// Birth year approximation
const birth = parse('1850~');

// Death somewhere in a range
const death = parse('1920/1925');

// Marriage season
const marriage = parse('1875-21');
// Spring 1875

Why Use EDTF?

1. Standardization: International standard maintained by Library of Congress
2. Precision: Express exactly what you know (and don't know) about a date
3. Interoperability: Share data consistently across systems and institutions
4. Expressiveness: Handle complex date scenarios that traditional formats can't
5. Machine-readable: Easy to parse and process programmatically
6. Human-friendly: Clear syntax that conveys meaning

Specification

The full EDTF specification is maintained by the Library of Congress:

• Official Specification (2019)
• Based on ISO 8601-2:2019

Next Steps

• Getting Started - Install and use EDTF-TS
• EDTF Levels - Detailed breakdown of each conformance level
• Examples - See EDTF in action