Dates in Citations

Two kinds of dates can be identified within the citation elements <element-citation> and <mixed-citation>:
  • the publication date of the cited resource, and
  • all other dates mentioned in the citation.
It is best practice to tag the publication date, which can be recorded using ordinary date tags such as <year>. Several of the date elements may be used in a citation, including <day>, <month>, and <season>. Typically, for cited journal articles, the citation will contain only a <year>: <year>2008</year>.
All other dates in the citations, if they are tagged, use the <date-in-citation> element, identifying the type of date with the @content-type attribute. For example, if the resource has a time stamp when it was posted (in addition to the regular publication date), the time stamp can be recorded as: <date-in-citation content-type="time-stamp"/>...</date-in-citation>.

Publication Date

Within bibliographic references (<element-citation> and <mixed-citation>), the most important date to tag for purposes of searching and making the citation into a live link is the publication date. The most common form of the date is the year (<year>), shown in the following citation which also includes the month:
<mixed-citation publication-type="journal" publication-format="print">
<name>...</name>. <article-title>Links between dietary salt ... and 
cardiovascular diseases</article-title>. <source>Physiol Rev</source>.
<year iso-8601-date="2005-04">2005</year> <month>Apr</month>;<volume>85</volume>
Multiple years may be tagged with separate <year> elements:
<mixed-citation publication-type="journal">...
<year iso-8601-date="2008">2008</year>&ndash;<year>2009</year>;  
or combined into a single year:
<mixed-citation publication-type="journal">...
<year iso-8601-date="2008">2008&ndash;2009</year>; 
In this Tag Set, the elements <date>, <day>, <month>, and <season> may all be used in addition to <year> to describe the publication date.
<element-citation publication-type="book">...
<season>Winter</season><year iso-8601-date="2008">2008</year>

<mixed-citation publication-type="book">... 
<season>Winter</season> <year iso-8601-date="2008">2008</year> 

Non-publication Dates

Within bibliographic citations (<element-citation> and <mixed-citation>), the <date-in-citation> element can be used to tag dates other than the publication date of the cited source, for example, the copyright date, the date on which the contributor accessed the source, the date the cited resource was withdrawn, or a time stamp indicating when the work was published, for continuously or frequently updated works. The @content-type attribute should be used to identify the purpose or type of date; for example, if the element contains the date on which the article was withdrawn, the value of the @content-type would be “withdrawn”.
Here is an example in which <date-in-citation> was used to record the date on which the cited work was last updated. If a resource has a time stamp in addition to a publication date, that time stamp could be recorded using this element with a @content-type attribute of “time-stamp”. Such a time stamp is applied to the resource by its creators, usually as a version indicator, and says nothing about when a contributor examined the resource, only what version was found at the time of examination. Some online resources are changing so quickly that a citation to the resource is not complete without the publication time of the resource. The @content-type should be used to identify such time-stamps:
<date-in-citation content-type="time-stamp" iso-8601-date="2014-01-11T11:57:00-5:00">
January 11, 2014 at 11:57am</date-in-citation> 
<date-in-citation content-type="time-stamp" iso-8601-date="2014-01-11T11:57:00-5:00">
January 11, 2014 at 11:57am</date-in-citation> 

Here is an example of the <date-in-citation> element used to record publication history dates that were noted in the citation:
<element-citation publication-type="book" publication-format="web">
<collab>CENDI Copyright Working Group</collab>
<source>Frequently asked questions about copyright ...</source>
<person-group person-group-type="editor">...</person-group>
...<year iso-8601-date="2004-08">2004</year><month>Aug</month>
<date-in-citation iso-8601-date="2005-09-02">modified 2006 Sep 2</date-in-citation>
<date-in-citation iso-8601-date="2005-11-06">cited 2006 Nov 6</date-in-citation>

<mixed-citation publication-type="book" publication-format="web">
<collab>CENDI Copyright Working Group</collab>. <source>Frequently 
asked questions about copyright: ...</source>  [Internet].
<person-group person-group-type="editor">...</person-group>, editors.
... <year iso-8601-date="2004-08">2004</year> <month>Aug</month>
[<date-in-citation iso-8601-date="2006-09-02">modified 2006 Sep 2</date-in-citation>;
<date-in-citation iso-8601-date="2005-11-06">cited 2006 Nov 6</date-in-citation>]. 
Unlike the <year> element as used in a publication date where best practice is to tag multiple years with multiple elements, multiple years in non-publication dates should be tagged in a single element.
<date-in-citation content-type="copyright" iso-8601-date="2004">2004
In a <mixed-citation>, the above date can be tagged as:
Copyright <date-in-citation content-type="copyright">2004-2009</date-in-citation>
In an <element-citation>, the same date could be tagged as follows or the word “Copyright” could be generated for display.
<date-in-citation content-type="copyright" iso-8601-date="2004">2004-2009</date-in-citation>

Copyright and Publication Together

When both a copyright year and a publication year are present in the same citation, the ordinary date tags (<date>, <day>, <month>, <season> and <year>) should be used to record the publication date. Here is a publication date tagged with <year>:
<year iso-8601-date="2007">2007</year>
In contrast, the copyright date is tagged with <date-in-citation>, naming the type of date as a copyright date in the attribute:
<date-in-citation content-type="copyright" iso-8601-date="2007">2007</date-in-citation>
But when there is a single date in the citation and it is the copyright date, a publisher or archive must choose whether to tag that single date using the <year> element or the <date-in-citation> element. The advantage of tagging that date as a year is that it gives the citation matching tools (which match on years) some handle on the date. Therefore, an archive might choose to tag the lone copyright date as:
<year content-type="copyright" iso-8601-date="2008">2008</year>
instead of using the <date-in-citation> element, as would be done when both dates were present.

Date Prefixes and Suffixes

Some citation dates are prefixed with one or more letters. Some publishers prefix the year with a copyright symbol or a lower case “c” meaning that this is a copyright date. In mixed-style citations, these symbols can be preserved directly in the text, between tagged elements:
<mixed-citation publication-type="book">... 
&copy;<year content-type="copyright" iso-8601-date="2004">2004</year>; 

<mixed-citation publication-type="book">... 
c<year content-type="copyright" iso-8601-date="2004">2004</year>; 
In an element-only style citation, the symbol or the letter should either be removed entirely and left for the display to infer from the content-type="copyright" or placed into a <comment> element.
<comment>&copy;</comment><year content-type="copyright" iso-8601-date="2004">2004</year>

<element-citation publication-type="book">... 
<year content-type="copyright" iso-8601-date="2004">2004</year>
In some books or older manuscripts, the lower case “c” could also stand for “circa”, meaning approximate. Similar information might be indicated by the prefix or suffix “approx.” or the prefix “between”. Such terms should be preserved similarly; they should be left in the text for mixed citations and placed in comments for element citations.