There are four entry types, corresponding to different granularities
in the identification of the (part of) software artifacts that one
whishes to cite. They are listed below in order of granularity.

\subsection{software}
Computer software. 

\emph{Required fields:} \texttt{author} / \texttt{editor}, \texttt{title}, \texttt{url}, \texttt{year}

\emph{Optional fields:} \texttt{abstract}, \texttt{date}, \texttt{doi}, \texttt{eprint}, \texttt{eprintclass}, \texttt{eprinttype}, \texttt{file}, \texttt{hal\_id}, \texttt{hal\_version},
\texttt{institution}, \texttt{license}, \texttt{month}, \texttt{note}, \texttt{organization}, \texttt{publisher},
\texttt{related}, \texttt{relatedtype}, \texttt{relatedstring}, \texttt{repository}, \texttt{swhid}, \texttt{urldate}, \texttt{version}

\subsection{softwareversion}
A specific version of a software.  Inherits values of missing
fields from the entry mentioned in the \texttt{crossref} field.

\emph{Required fields:} \texttt{author} / \texttt{editor}, \texttt{title}, \texttt{url}, \texttt{version}, \texttt{year}

\emph{Optional fields:} \texttt{abstract}, \texttt{crossref}, \texttt{date}, \texttt{doi}, \texttt{eprint}, \texttt{eprintclass}, \texttt{eprinttype}, \texttt{file}, \texttt{hal\_id}, \texttt{hal\_version},
\texttt{institution}, \texttt{introducedin}, \texttt{license}, \texttt{month}, \texttt{note}, \texttt{organization}, \texttt{publisher},
\texttt{related}, \texttt{relatedtype}, \texttt{relatedstring}, \texttt{repository}, \texttt{swhid}, \texttt{subtitle}, \texttt{urldate}

\subsection{softwaremodule}

A specific module of a larger software project. Inherits values of missing
fields from the entry mentioned in the \texttt{crossref} field.

\emph{Required fields:} \texttt{author}, \texttt{subtitle}, \texttt{url}, \texttt{year}

\emph{Optional fields:} \texttt{abstract}, \texttt{crossref}, \texttt{date}, \texttt{doi}, \texttt{eprint}, \texttt{eprintclass}, \texttt{eprinttype}, \texttt{editor}, \texttt{file}, \texttt{hal\_id}, \texttt{hal\_version},
\texttt{institution}, \texttt{introducedin}, \texttt{license}, \texttt{month}, \texttt{note}, \texttt{organization}, \texttt{publisher},
\texttt{related}, \texttt{relatedtype}, \texttt{relatedstring}, \texttt{repository}, \texttt{swhid}, \texttt{title}, \texttt{urldate}, \texttt{version}

\subsection{codefragment}

A code fragment (e.g. a specific algorithm in a program or library).
Inherits values of missing fields from the entry mentioned in the \texttt{crossref} field.

\emph{Required fields:}  \texttt{url}

\emph{Optional fields:} \texttt{author}, \texttt{abstract}, \texttt{crossref}, \texttt{date}, \texttt{doi}, \texttt{eprint}, \texttt{eprintclass}, \texttt{eprinttype}, \texttt{file}, \texttt{hal\_id}, \texttt{hal\_version},
\texttt{institution}, \texttt{introducedin}, \texttt{license}, \texttt{month}, \texttt{note}, \texttt{organization}, \texttt{publisher},
\texttt{related}, \texttt{relatedtype}, \texttt{relatedstring}, \texttt{repository}, \texttt{swhid}, \texttt{subtitle}, \texttt{title}, \texttt{urldate}, \texttt{version}, \texttt{year}

The \textbf{softwareversion}, \textbf{softwaremodule} and \textbf{codefragment} entries can inherit
the missing fields from another entry designated by the \emph{crossref} field, which
is expected to be higher in the granularity hierarchy: \textbf{softwareversion} may
inherit from a \textbf{software} entry, \textbf{softwaremodule} may inherit from a
\textbf{softwareversion} or a \textbf{software} entry, and \textbf{codefragment} may inherit from all
other entries.

\section{Field description}
The field description is based on the \href{http://mirrors.ibiblio.org/CTAN/macros/latex/exptl/biblatex/doc/biblatex.pdf}{biblatex documentation}
\subsection{Data fields}
\begin{description}
\item[{abstract}] field (literal). This field is intended for recording 
abstracts in a bib file, to be printed by a special bibliography 
style. It is not used by all standard bibliography styles.
\item[{author}] list (name). The authors of the title.
\item[{date [biblatex only]}] field (date). The date of creation or release in ISO format.
\item[{editor}] list (name). The coordinator(s) of large modular software projects.
\item[{file}] field (verbatim). A link to download a copy of the work.
\item[{doi}] field (verbatim). The Digital Object Identifier of the work.
\item[{eprint [biblatex only]}] field (verbatim). An electronic identifier of the work. This field can be used to accommodate electronic identifiers different from the ones that have a dedicate field in this style.
\item[{eprinttype [biblatex only]}] field (verbatim). The type of eprint identifier, e. g., the name of the archive, repository, service, or system the eprint field refers to. Will be typeset by default as a prefix of the content of the eprint field.
\item[{eprintclass [biblatex only]}] field (verbatim). Additional information related to the resource indicated by the eprinttype field. This could be a section of an archive, a path indicating a service, a classification of some sort.
\item[{\texttt{hal\_id} [not in biblatex standard styles]}] field (verbatim). A digital identifier for the 
software record including its description and metadata on HAL.
\item[{\texttt{hal\_version} [not in biblatex standard styles]}] field (verbatim). The version of the HAL software record designated by \texttt{hal\_id}.
\item[{license [not in biblatex standard styles]}] list (literal). The license/s of the title 
in SPDX format.
\item[{month}] field (literal). The month of creation or release. 
In BibLaTeX, this must be an integer, not an ordinal or a string.
For compatibility with BibTeX, one can also use the three letter
abbreviations \emph{jan, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec},
which must be given without any braces or quotes.
\item[{note}] field (literal). Release note of the cited version.
\item[{institution}] list (literal). The institution(s) that took part in the software project.
\item[{introducedin [not in biblatex standard styles]}] field (literal). If this is a software module or fragment,
the version of the containing project where it has been first introduced.
\item[{organization}] list (literal). The organization(s) that took part in the software project.
\item[{publisher}] list (literal). The name(s) of the publisher(s) of the \emph{qualified} software record.
\item[{related [biblatex only]}] field (separated values). Citation keys of other entries which have a relationship to this entry.
\item[{relatedtype [biblatex only]}] field (identifier).
\item[{relatedstring [biblatex only]}] field (literal).
\item[{repository [not in biblatex standard styles]}] field (uri). The url of the code repository (e.g on GitHub, GitLab).
\item[{swhid [not in biblatex standard styles]}] field (verbatim). The identifier of the digital
object (a.k.a the software artifact itself). The intrinsic identifier
of the item is an swh-id (swh:cnt for a content, swh:dir for a directory, swh:rev for
a revision, swh:rel for a release, etc.). See \href{https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html}{the SWH-ID specification}.
\item[{subtitle}] field (literal). The title of a component of the software artifact.
\item[{title}] field (literal). The title of the software artifact.
\item[{url}] field (uri). The url of a reference resource (e.g the project's official webpage).
\item[{urldate}] field (date). The access date of the address specified in the url field.
\item[{version}] field (literal). The revision number of a piece of software, a manual, etc.
\item[{year}] field (literal). The year of creation or release.
\end{description}
\subsection{Special fields}
\begin{description}
\item[{crossref}] field (entry key). This field holds an entry key for the
cross-referencing feature. Child entries with a crossref field inherit data
from the parent entry specified in the crossref field.
\end{description}

\section{Examples}

Here are a few example of use of the proposed entries.

\subsection{software and softwareversion}

This is an example description of a software release using a single \texttt{@softwareversion} entry.

\begin{verbatim}
@softwareversion {delebecque:hal-02090402-condensed,
  title = {Scilab},
  author = {Delebecque, Fran{\c c}ois and Gomez, Claude and Goursat, Maurice 
    and Nikoukhah, Ramine and Steer, Serge and Chancelier, Jean-Philippe},
  url = {https://www.scilab.org/},
  date = {1994-01},
  file = {https://hal.inria.fr/hal-02090402/file/scilab-1.1.tar.gz},
  institution = {Inria},
  license = {Scilab license},
  hal_id = {hal-02090402},
  hal_version = {v1},
  swhid = {swh:1:dir:1ba0b67b5d0c8f10961d878d91ae9d6e499d746a;
	   origin=https://hal.archives-ouvertes.fr/hal-02090402},
  version = {1.1},
  note = {First Scilab version. It was distributed by anonymous ftp.},
  repository= {https://github.com/scilab/scilab},
  abstract = {Software for Numerical Computation freely distributed.}
}
\end{verbatim}

The same information can also be represented using a \texttt{@software} / \texttt{@softwareversion}
pair that factors out the general information in the \texttt{@software} entry, so for
other versions only the changes need to be added in a new \texttt{@softwareversion} entry:

\begin{verbatim}
@software {delebecque:hal-02090402,
  title = {Scilab},
  author = {Delebecque, Fran{\c c}ois and Gomez, Claude and Goursat, Maurice 
    and Nikoukhah, Ramine and Steer, Serge and Chancelier, Jean-Philippe},
  date = {1994},
  institution = {Inria},
  license = {Scilab license},
  hal_id = {hal-02090402},
  hal_version = {v1},
  url = {https://www.scilab.org/},
  abstract = {Software for Numerical Computation freely distributed.},
  repository= {https://github.com/scilab/scilab},
}

@softwareversion {delebecque:hal-02090402v1,
  version = {1.1},
  date = {1994-01},
  file = {https://hal.inria.fr/hal-02090402/file/scilab-1.1.tar.gz},
  swhid = {swh:1:dir:1ba0b67b5d0c8f10961d878d91ae9d6e499d746a;
	   origin=https://hal.archives-ouvertes.fr/hal-02090402},
  note = {First Scilab version. It was distributed by anonymous ftp.},
  crossref = {delebecque:hal-02090402}
}
\end{verbatim}

\subsection{softwaremodule}

For highly modular software projects, like CGAL, one may need to 
reference specifically a particular module, that has distinguished
authors, and may heve been introduced in the project at a later time.


The following example uses \href{https://doc.cgal.org/latest/Manual/how\_to\_cite\_cgal.bib}{the informations in the existing BibTeX entries for CGAL}
that currently refer to the user manual, to create the corresponding software entries.

\begin{verbatim}
@software {cgal,
 title = {The Computational Geometry Algorithms Library},
 author = {{The CGAL Project}},
 editor = {{CGAL Editorial Board}},
 date = {1996},
 url = {https://cgal.org/}
}

@softwareversion{cgal:5-0-2,
 crossref = {cgal},
 version = {{5.0.2}},
 url = {https://docs.cgal.org/5.02},
 date = {2020},
 swhid = {swh:1:rel:636541bbf6c77863908eae744610a3d91fa58855;
	  origin=https://github.com/CGAL/cgal/}
}

@softwaremodule{cgal:lp-gi-20a,
 crossref = {cgal:5-0-2},
 author = {Menelaos Karavelas},
 subtitle = {{2D} Voronoi Diagram Adaptor},
 license = {GPL},
 introducedin = {cgal:3-1},
 url = {https://doc.cgal.org/5.0.2/Manual/packages.html#PkgVoronoiDiagram2},
}
\end{verbatim}

Of course, it is always be possible to use only one entry to get an equivalent
result; here one would use just \texttt{@softwaremodule} with all the needed data
fields as follows:

\begin{verbatim}
@softwaremodule{cgal:lp-gi-20a-condensed,
 title = {The Computational Geometry Algorithms Library},
 subtitle = {{2D} Voronoi Diagram Adaptor},
 author = {Menelaos Karavelas},
 editor = {{CGAL Editorial Board}},
 license = {GPL},
 version = {{5.0.2}},
 introducedin = {cgal:3-1},
 date = {2020},
 swhid = {swh:1:rel:636541bbf6c77863908eae744610a3d91fa58855;
	  origin=https://github.com/CGAL/cgal/},
 url = {https://doc.cgal.org/5.0.2/Manual/packages.html#PkgVoronoiDiagram2},
}
\end{verbatim}

\subsection{codefragment}

Finally, if one wants to have a particular code fragment appear in the bibliography,
we can do this as follows:
\begin{verbatim}
@software {parmap,
  title = {The Parmap library},
  author = {Di Cosmo, Roberto and Marco Danelutto},
  date = {2012},
  institution = {{Inria} and {University of Paris} and {University of Pisa}},
  license = {LGPL-2.0},
  url = {https://rdicosmo.github.io/parmap/},
  repository= {https://github.com/rdicosmo/parmap},
}

@softwareversion {parmap-1.1.1,
  crossref = {parmap},
  date = {2020},
  version = {1.1.1},
  swhid = {swh:1:rel:373e2604d96de4ab1d505190b654c5c4045db773;
     origin=https://github.com/rdicosmo/parmap;
     visit=swh:1:snp:2a6c348c53eb77d458f24c9cbcecaf92e3c45615},
}

@codefragment {simplemapper,
  subtitle = {Core mapping routine},
  swhid = {swh:1:cnt:43a6b232768017b03da934ba22d9cc3f2726a6c5;
     origin=https://github.com/rdicosmo/parmap;
     visit=swh:1:snp:2a6c348c53eb77d458f24c9cbcecaf92e3c45615;
     anchor=swh:1:rel:373e2604d96de4ab1d505190b654c5c4045db773;
     path=/src/parmap.ml;
     lines=192-228},
  crossref = {parmap-1.1.1}
}
\end{verbatim}

Of course, it is always be possible to use only one entry to get an equivalent
result; here one would use just \texttt{@codefragment} with all the needed data
fields as follows:

\begin{verbatim}
@codefragment {simplemapper-condensed,
  title = {The Parmap library},
  author = {Di Cosmo, Roberto and Marco Danelutto},
  date = {2020},
  institution = {{Inria} and {University of Paris} and {University of Pisa}},
  license = {LGPL-2.0},
  url = {https://rdicosmo.github.io/parmap/},
  repository= {https://github.com/rdicosmo/parmap},
  version = {1.1.1},
  subtitle = {Core mapping routine},
  swhid = {swh:1:cnt:43a6b232768017b03da934ba22d9cc3f2726a6c5;
     origin=https://github.com/rdicosmo/parmap;
     visit=swh:1:snp:2a6c348c53eb77d458f24c9cbcecaf92e3c45615;
     anchor=swh:1:rel:373e2604d96de4ab1d505190b654c5c4045db773;
     path=/src/parmap.ml;
     lines=192-228}
}
\end{verbatim}