Citations and References

Overview

Questions

• How do I add bibliographic references to my document?
• How do I format my references in LaTeX?
• How do I cite references in my document?

Objectives

• Learn how to use a reference database to manage references in LaTeX documents.
• Explore different ways of citing references in our document.

Citations and References

---

For bibliographic citations, while you can include references sources directly in our document, usually you will get that information from one or more external files. Such a file is a database of references, containing the information in a processing-friendly format (which is called BibTeX). Using one or more reference databases lets you re-use information and avoid manual formatting.

Settings

---

TeXstudio offers several backend options for handling BibTeX files. For the purposes of this workshop, we’ll use Biber. Open TeXstudio and go to Options > Configure TeXstudio. In the configuration dialog, select Build from the left-hand panel. Under Default Bibliography Tool, open the drop-down menu and select Biber.

Reference Databases (BiBTeX)

---

Reference databases are normally referred to as BiBTeX files, and have the extension .bib. They contain one or more entries, one for each reference, and within each are a series of fields.

Create a new file in your project called sample-references.bib and add the following content:

BIBTEX

@article{Thomas2008,
	author  = {Thomas, Christine M.},
	title   = {The Fascinating World of Penguins},
	journal = {Penguin Chronicles},
	date    = {2008},
	pages   = {7009-7024},
}

@book{Graham1995,
	author    = {Graham, Richard L. and Harris, Lisa A.},
	title     = {The Humble Paperclip},
	subtitle  = {Master of the Modern Office},
	publisher = {Scranton Press},
	year      = {1995},
}

This is an example of a BiBTeX file that contains a reference for an article and another for a book. Each entry type starts with a the @ symbol, followed by the type of the referencing item (e.g. article) and all information appears within a pair of curly braces {}.

The various fields are given in key-value format. Exactly which fields you need to give depends on the type of entry.

Callout

You might notice that in the author field, surname and givenname and each entry (author) is separated by the word and. This is essential: the format of the output needs to know which author is which. When using biblatex this applies also to the fields publisher and location, in which you can also have many values.

You might also notice that in the article title, some entries are in an extra set of braces. This is to prevent any case-changing that might be applied to the title.

The BibTeX Format

Editing BiBTeX files by hand can be difficult and tedious. A number of tools exist to help you manage your reference files. You can find a list of sugggested tools in the references section.

For the purposes of this workshop, we’ll use biblatex, but feel free to explore other options (e.g. natbib) on your own.

biblatex

Good to know

Check to make sure that your main.tex file is in the same directory as your sample-references.bib file.

At the top of our main.tex file, we’ll add a line to import biblatex:

LATEX

\usepackage[style=authoryear]{biblatex}
\addbibresource{sample-references.bib}

Do not forget to write the suffix of your referencing file, too (.bib).

Then, at the bottom of your main.tex file, add the following lines:

LATEX

\printbibliography

And… nothing? Right, because we haven’t cited anything in our document yet. Let’s add a citation:

LATEX

\section{Reference Databases}

We can \kw{cite references} from our bibliography.

We can cite the article by Thomas (e.g. with `\textbackslash autocite\{Thomas2008\}`).

You should see that the citation appears in the text ((Thomas et al. 2008)), and the reference now appears at the end of the document. is a command that automatically chooses the citation style for you.

Some additional commands that are available in biblatex:

• \cite{key} or \cite{key1, key2}: Cite the reference with the given key
• \usepackage{}\parentcite{key}: Cite the parent reference of the given key.
• \autocite{key}: Automatically choose the citation style.
• \smartcite{key}: Automatically choose the citation style, but with more control.
• \footcite{key}: Cite the reference in a footnote.

A plain citation looks like this \cite{Graham1995}, while multiple citations look like this \cites{Graham1995}[see][p. 42]{Thomas2008}. We already used autocite, but we can also use the similar smartcite \smartcite{Graham1995}. The benefit with smartcite is that you can setup that e.g. all references should go into a footnote. You can continue using smartcite when you are in a footnote and it will then detect that there is no need for creating another footnote but behaving like autocite.

Furthermore you can use more commands to get the author, title or the date of the publication directly into your document:

• \citeauthor{Graham1995}: Graham and Harris
  
• \citetitle{Graham1995}: “The Humble Paperclip”
  
• \citeyear{Graham1995}: 1995

The outcome and display depends on your style.

If you want to have all entries of your referencing file in your bibliography, you can either go with \cite{key1,key2,.....} for all entries or you type \cite{*}. This will print all entries first in your text section and puts them into the bibliography. You can also go with \nocite{*} then the reference is only internally called and put into the bibliography.

It is always good to tidy up your .bib-file and use the fields accordingly. In case you want to omit certain fields in your bibliography you can do so on the fly:

LATEX

\AtEveryBibitem{
  \clearfield{url}
  \clearfield{month}
  \clearfield{note}
  \clearfield{isbn}
  \clearname{translator}
  \clearlist{language}
}

With this command you will delete the content of the fields in the bibliography. Note, that there is \clear*field*, \clear*name* and \clear*list*.

Callout

There are many different bibliography styles available, and you can find a list of them at CTAN. Check if one of those bibligraphy and citation styles meets your requirements. If you want to finetune an existing one we suggest to take a look at biblatex-ext.

Challenges

---

Challenge

Challenge 1: Add another reference, then delete it.

Try adding the following reference to your sample-references.bib file:

BIBTEX

@book{Huff1954,
  author    = {Huff, Darrell},
  title     = {How to Lie with Statistics},
  publisher = {W. W. Norton \& Company},
  year      = {1954},
}

Then, add a citation to this reference in your document. Try a couple different styles of citation commands. Then, once you have it working, delete the reference and re-compile your document. What happens?

Show me the solution

You might expect removing the reference to either error or remove the citation from the text, but it doesn’t - instead we get a placeholder in the text and a warning in the log. A missing reference is not so critical an error that we can’t render the document, but we should probably fix it.

Challenge

Challenge 2: What’s wrong with this?

We have the following reference in our document:

BIBTEX

@misc{mikolov2013,
	title         ={Efficient Estimation of Word Representations in Vector Space},
	author        ={Mikolov, Tomas and Chen, Kai and Corrado, Greg and Dean, Jeffrey},
	year          ={2013},
	eprint        ={1301.3781},
	archivePrefix ={arXiv},
	primaryClass  ={cs.CL},
	url           ={https://arxiv.org/abs/1301.3781},
}

We are using biblatex to manage our references, and we identify this reference in the text like this:

LATEX

The Word2Vec algorithm \autocite{mikolov} is a popular method for generating word embeddings.

When we compile our document, we see the following error:

OUTPUT

The Word2Vec algorithm (mikolov) is a popular method for generating word embeddings.

What’s wrong with this reference? How can we fix it?

Show me the solution

We are referencing the key mikolov in our document, but the key in our BiBTeX file is mikolov2013. We need to update our citation command to \autocite{mikolov2013}. Note that LaTeX still compiles the document, but it gives us a warning that the reference is missing and uses the key as a placeholder. You might use this to temporarily mark a reference that you haven’t added yet, just be sure to clear all of your warnings before finializing your document.

Challenge

Challenge 3: What’s problem with this?

We inculde the following reference in our document:

BIBTEX

@article{bentham2011,
	author = {H. Muller, Rainer and Shegokar, Ranjita and M. Keck, Cornelia},
	title = {20 Years of Lipid Nanoparticles (SLN & NLC): Present State of Development & Industrial Applications}, 
	journal= {Current Drug Discovery Technologies},
	year = {2011},
	volume = {8},
	number = {3},
	pages = {207--227},
	doi = {https://doi.org/10.2174/157016311796799062},
	publisher = {Bentham Science Publishers},
}

We are using biblatex and cite this reference in the text as follows:

LATEX

\autocite{bentham2011} provied a good overview over nanoparticles over the last 20 years.

What happens when compiling this document? What is wrong with the reference, and how can it be fixed?

Show me the solution

The issue in this reference is cause by a sepcial character (& in the title field). In LaTeX the ampersand & is reserved for alignment, so it must be escaped (\&)in normal text.

If special characters are not escaped properly, LaTeX produce unexpected output or may fail to compile. In some cases, this can also corrupt auxiliary files (such as .aux or .bbl), preventing the document from rendering as expected. If problems persist after correcting the reference, a common solution is to delete all intermediate files and recompile the document from scratch. Deleting them forces a clean rebuild.

Corrected bib entry:

BIBTEX

@article{bentham2011,
	author = {H. Muller, Rainer and Shegokar, Ranjita and M. Keck, Cornelia},
	title = {20 Years of Lipid Nanoparticles (SLN \& NLC): Present State of Development \& Industrial Applications}, 
	journal= {Current Drug Discovery Technologies},
	year = {2011},
	volume = {8},
	number = {3},
	pages = {207--227},
	doi = {https://doi.org/10.2174/157016311796799062},
	publisher = {Bentham Science Publishers},
}

Key Points

• References are stored in a reference database, seperate from the LaTeX document.
• BiBTeX files are used to store references in a processing-friendly format and have the extension .bib.
• There are multiple libraries available to manage references in LaTeX documents, including natbib and biblatex.
• We can use the \cite command or one of its variants to cite references in our document.