Encoding Unit Dates

Schema: EAD 4.0

Context: Encoding dates of described materials within <identificationData>

Description: Use <unitDate> and its sub-elements to encode dates when the described materials were created, issued, copyrighted, broadcast, etc. Where possible, follow agreed national or local conventions (such as the US DACS standard) for expressing dates consistently.

<unitDate> must contain one of the following sub-elements: <date>, <dateRange>, <dateSet> and <textualDate>.

Use <date> to encode a single date in human- and machine-readable form. State the human-readable date as the content of the element. Provide a machine-readable date using the @standardDate attribute, formulated according to ISO 8601 or another rule.

For machine-readable uncertain or approximate dates, use Extended Date/Time Format (EDTF) in @standardDate or use @notBefore and @notAfter to capture the earliest and latest possible dates.

Use <dateRange> and its sub-elements <fromDate> and <toDate> to encode a range of dates in human- and machine-readable form. <dateRange> must contain either <fromDate> or <toDate>. Whenever possible, use both sub-elements: <fromDate> first, followed by <toDate>.

Use <fromDate> for the beginning of a date range and use <toDate> for the end of a date range. In both cases, state the human-readable date as the content of the element. Provide machine-readable dates using the @standardDate attribute, formulated according to ISO 8601 or another rule.

For machine-readable uncertain or approximate dates within <fromDate> and <toDate>, use @standardDate or @notBefore and @notAfter in the same manner as for <date>.

If the date range is open-ended (for instance, if there are frequent accruals of later materials), either omit <toDate> or use <toDate> with the @status attribute with the value “ongoing”.

Use <dateSet> to encode more complex dates in human- and machine-readable form. Such dates consist of two or more distinct single dates or date ranges. Only use <dateSet> where it is appropriate to encode complex date information in this degree of granularity.

<dateSet> requires at least two sub-elements: either two instances of <date>, two instances of <dateRange> or one instance of each. More than two can be used (in any combination) if required.

Use <textualDate> for free text statements of human-readable dates. These do not need to be expressed in a standardized or structured way. Date-specific attributes (@dateChar, @calendar, @certainty, @era, @notAfter, @notBefore or @standardDate) are not allowed within <textualDate>.

When used as children of <unitDate>, <date>, <dateRange> and <dateSet> are not repeatable and cannot be used together. Choose one of them and use it once. However, <date> and <dateRange> are repeatable if used as children of <dateSet>.

• For a single date, use <date>
• For one discrete range of dates, use <dateRange>
• To use <date> and <dateRange> together or to repeat either element, nest them within <dateSet>

<textualDate> may be used as a child of <unitDate>, either alone or alongside <date>, <dateRange> or <dateSet>. <textualDate> is not allowed within <dateSet>.

Example: A single date encoded using <date>

<identificationData>
  <unitDate>
    <date certainty="circa" standardDate="1973">circa 1973</date>
  </unitDate>
</identificationData>

Example: A date range encoded using <dateRange> alongside a free-text statement in <textualDate>

<identificationData>
  <unitDate>
    <dateRange>
        <fromDate standardDate="1988-11-01"/>  
        <toDate standardDate="2001-10-31"/>
    </dateRange>
    <textualDate>November 1988 through October 2001</textualDate>
  </unitDate>
</identificationData>

Example: A single date encoded using <date> alongside an alternative date format encoded using <textualDate>

<identificationData>
  <unitDate>
    <date standardDate="1617-11-03">1617 November 3</date>
    <textualDate>15 James 1, Morrow of All Souls</textualDate>
  </unitDate>
</identificationData>

Example: A complex date encoded using <dateSet> (with child elements <dateRange> and <date>) and <textualDate>

<identificationData>
  <unitDate>
    <dateSet>
      <date standardDate="1815~"></date>
      <dateRange>
        <fromDate standardDate="1819"></fromDate>
        <toDate standardDate="1825"></toDate>
      </dateRange>
      <date standardDate="1830"></date>
    </dateSet>
    <textualDate>approximately 1815, 1819-1825, 1830</textualDate>
  </unitDate>
</identificationData>