Why and when to cite

A citation tells the reader where an idea, fact or piece of work came from.

The two halves of a citation

Every citation has two parts that point to each other:

1. In-text citation: a short marker where you use the source, like (Keshav, 2007) or [1].
2. Reference entry: the full details in the reference list at the end: authors, year, title, where it was published, and a link.

The marker says "this came from somewhere". The entry says exactly where, so anyone can find it.

The DOI

Most papers have a DOI (Digital Object Identifier), like 10.1145/1273445.1273458. Put https://doi.org/ in front and it always opens the paper, even if the publisher's website changes. Include the DOI in your reference entries whenever there is one.

Why cite

• Credit. It gives credit to the people whose work you used.
• Checking. It lets readers check your sources for themselves.
• Context. It shows where your work fits.
• Honesty. Not citing someone's work and presenting it as your own is plagiarism.

Cite when you use

• someone's ideas or arguments, even in your own words
• facts or numbers that are not common knowledge
• exact words (in quotation marks)
• figures, tables or images (and check the licence before you reuse them)
• datasets, code and models you used: in AI, these count as sources too
• a method someone else created

You do not need to cite

• Common knowledge in your field: facts any reader would know and that can be found in many general sources. "Python is a programming language." When in doubt, cite.
• Your own new results and ideas in this paper.

Cite the source you actually read

If you read about a 1950 paper in a 2020 survey, and never read the 1950 paper, you should be careful about citing it directly. Ideally, find and read the original. At the least, be sure the claim you attach to it is really in it. Many wrong "facts" spread because people cite papers they never opened.

RememberIf a reader could reasonably ask "says who?", you need a citation.