Online sources without “last edited” date field

Question

My university requires online sources to include three different dates per entry:

1. Date of original publication
2. Date of last edit
3. date of visiting the website

Well, the first and third date are easy, but what biblatex field corresponds to the second date?

1. date
2. ???
3. urldate

In the end, an entry should look something like

Uthor, A. (1996): A Stackexchange question. <https://tex.stackexchange.com/questions/ask>. (Last edited: 2008-04-36) (Last checked: 2018-01-29)

where the dates correspond to the above definitions as

1. 1996
2. 2008-04-36
3. 2018-01-29

How do I approach this? Right now, I just use the note field, but, of course, this is not exactly desirable, since it is not very "clean".

EDIT: just found some other similar questions. I need to work on that, although I have not much knowledge as to which bibmacro I need to edit or, actually, about adding custom fields to entries and incorporating them in macros. I'll see what I can do.

• biblatex format for online sources

• What is the best way to handle bibliographies which include a lot of online sources?

• Biblatex: Custom date fields

I shall investigate them further.

Answer 1

Similar to Biblatex: Custom date fields. We need to define a .dbx file to make the new lasteditdate known to Biber. Then we only need to add a call to \printlasteditdate to the URL/URL date macro.

\RequirePackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@online{elk,
  author       = {Anne Elk},
  title        = {On the Theory of Brontosauruses},
  url          = {https://example.edu/~elk/bronto.html},
  lasteditdate = {2018-01-15},
  urldate      = {2018-01-29},
}
\end{filecontents*}


\begin{filecontents*}{lastedit.dbx}
\DeclareDatamodelFields[type=field, datatype=date, skipout]{
  lasteditdate,
}
\DeclareDatamodelEntryfields{
  lasteditday,
  lasteditendday,
  lasteditendhour,
  lasteditendminute,
  lasteditendmonth,
  lasteditendsecond,
  lasteditendtimezone,
  lasteditendyear,
  lastedithour,
  lasteditminute,
  lasteditmonth,
  lasteditsecond,
  lastedittimezone,
  lastedityear,
}
\end{filecontents*}

\documentclass[british]{article}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[backend=biber, datamodel=lastedit, lasteditdate=short]{biblatex}
\usepackage{hyperref}
\addbibresource{\jobname.bib}

\NewBibliographyString{lastchanged}
\DefineBibliographyStrings{english}{
  lastchanged = {last changed},
}

\DeclareFieldFormat{lasteditdate}{\mkbibparens{\bibstring{lastchanged}\space#1}}

\renewbibmacro*{url+urldate}{%
  \usebibmacro{url}%
  \iffieldundef{lastedityear}
    {}
    {\setunit*{\addspace}%
     \printlasteditdate}%
  \iffieldundef{urlyear}
    {}
    {\setunit*{\addspace}%
     \usebibmacro{urldate}}}

\begin{document}
\nocite{*}

\printbibliography
\end{document}

Answer 2

I can't comment yet, but it should be noted that the .dbx file @moewe created in the TeX should be named the same as the datamodel attribute given to biblatex. It will throw the following error (or something alike) when you try to run the biber %.bcf command: ! Package xkeyval Error: `lasteditdate' undefined in families `blx@opt@pre'.

Hope this saves someone the hour of debugging I just spent on it.

Note to the mods: I am aware this should be a comment on the accepted answer. I simply can't make comments yet :-)