The Photonics Spotlight > 2023-11-16

Citing Encyclopedia Articles

The RP Photonics Encyclopedia, a comprehensive resource on photonics and laser technology, has become an invaluable and widely used tool for researchers and professionals in the field. Our servers register about a quarter million page views per month on the encyclopedia. Presumably, these articles are often quite relevant to research and resulting publications. This raises the question of when and how encyclopedia articles should be cited. In this article, I present some thoughts on such matters, and also address various concerns. I also present some interesting news about the encyclopedia that is particularly relevant to citations.

Acknowledging Used Inputs

Basic rules of publication ethics require authors to cite those materials they use that are specifically relevant, for example, to a new research article in a scientific journal or wherever such materials are published. What exactly “specifically relevant” means requires some interpretation in specific cases.

A citation is not required when an input document contains only general background information that is already well known in the field. This will often be the case for an encyclopedia, which by its nature tends to focus on relatively fundamental aspects. Even if a newcomer learns about something for the first time by reading an encyclopedia article, this is not sufficient reason to cite it in a later paper – although there may be other reasons to cite it, as discussed below.

In some cases, however, the encyclopedia provides details that are not so well known; this is especially true for certain topics in laser physics and ultrashort pulses. In these cases, it would really be appropriate, if not necessary, to cite the source – especially if you cannot easily find an original research article presenting this knowledge.

Usefulness for the Readers

Citation decisions are not all about fairness; usefulness to readers is another very important aspect, although it sometimes seems to be overlooked. The primary purpose of a paper should be to contribute to the development of the field, i.e. to help the relevant research community, and not just to advance one's own career. If a reference to an encyclopedia article can be expected to be very useful not only for the author, but also for his or her readers, this is a strong argument for doing so.

Is Peer Review Required?

My encyclopedia articles, like most other encyclopedia articles, have not been peer-reviewed. This does not mean that they cannot be cited in scientific publications:

What counts in the end is quality and reliability. Peer review is just one of many methods to achieve this. As we all know, it is a rather imperfect method for various reasons, mainly because some reviewers do not do a good job. (Lack of payment and recognition for this important work, apart from limitations of competence or even some bias, are possible reasons.) Overall, peer review is certainly important, but it is neither sufficient to guarantee high quality nor indispensable in all circumstances:

• There are many scholarly textbooks that have not gone through a formal peer-review process and are still highly valued. If they are worth writing, printing, buying, and reading, why not cite them? Many would agree that my encyclopedia articles are clearly in the same category.
• Peer review may be especially desirable for certain controversial topics. For example, if someone wants to overturn an established theory, we want it to be reviewed by some hopefully unbiased experts before it is published in a scientific journal. However, such things don't normally happen in an encyclopedia – it's not a place for controversial discussions.

Open Access

The open access model is actually also relevant to citations, since it obviously affects the usefulness to readers. You can generally consider the open access nature of a publication as a positive argument for using it in a citation, although of course it is not a mandatory requirement. And the RP Photonics Encyclopedia is open access and will most likely remain so forever.

What about the online nature?

Print and online publications differ in some respects; is this relevant to the question of whether something is suitable for citation? At first glance, one might simply say no – it is the content that counts, and thus all factors that influence the quality of that content, but not the medium in which it is disseminated. But one should not overlook an important aspect: printed materials are immutable, i.e. they do not change after publication, while online resources can generally be modified later. Well, at least the content of a scientific journal article will not change, whether it is published in print or online, because that is a convention. At this point, my encyclopedia articles are different: they can be, and often are, changed.

Let us consider the implications of this, especially for citations:

• It can be seen as problematic that you, as an author, can only see such an article in its current form, but cannot know what will happen to it later. What if you cite it and a year later its content has changed completely, even saying things that contradict the original version? That could mislead your readers. However, this is highly unlikely – not only because an expert who enjoys the community's trust is unlikely to write things he will no more believe in later, but also because the focus on fundamental topics that is characteristic of an encyclopedia makes the need for such changes unlikely. The correct way to deal with this is simply to add the date of access to your citation, so that readers know that you mean the article as it was retrieved on that date. As a result, they cannot hold you responsible for endorsing content that may have been slightly different at earlier times. Furthermore, in such rare instances, I intend to leave a remark in the article, saying that an earlier version had a factual error which was corrected at a certain date.
• Furthermore, I emphasize that immutability (of journal articles, for example) also has significant drawbacks. For example, if a mistake is made, it can never be corrected, and even if an erratum is published, that can easily be overlooked.

• In fact, the quality of the RP Photonics Encyclopedia is largely due to my (much used!) freedom to improve the articles at any time. Errors can be corrected, explanations can be made clearer, relevant details including new references can be added, so that the articles not only stay up to date, but generally improve in various aspects of quality. The achieved quality and reliability of the content largely results from that, and not only from my qualities as a physicist and author.

Therefore, in my opinion, the mutability of my articles is (a) a minor problem and (b) a major advantage, and thus no reason to consider these articles as not citable.

Long-term Accessibility with DOI Links

Probably more important than content immutability is long-term accessibility. This has often been a concern of researchers considering to cite our articles. Partly for this reason, this week I have implemented a major improvement to the encyclopedia: I have given each encyclopedia article (and the encyclopedia itself) a Digital Object Identifier (DOI), which becomes part of a DOI link. For this purpose, RP Photonics has become a member of Crossref. More details about DOIs, the use of these links and the general concept can be found on a separate page.

The introduction of DOI links is a significant step forward for scholarly citation. Basically, it is a tool for ensuring long-term accessibility, among other benefits. Even if the entire encyclopedia were to move to another domain (for example, if some institution were to eventually buy the rights to the encyclopedia), the DOI links would still work without change, since the URLs stored in the DOI system would be updated.

The DOIs, by the way, are immutable, although the content of the articles is not. By assigning a DOI to an article, we promise to keep it available, and in fact we could not change the DOI.

Of course, this is no way to technically guarantee that the content will remain available until the end of our planet. But what other medium could guarantee that? Of course, we at RP Photonics have every intention of keeping the encyclopedia available, especially with the open access model that works so well for the community and for us.

Of course, the credibility of the content cannot be based on the presence of a DOI. However, people would generally trust that Crossref members don't publish garbage and have a genuine intention to keep their published material available.

How to Cite?

The format of citations can vary quite a bit, for example due to the standards of different journals. But in general, you need to give the author(s), the title, and some indication of where it can be found. In the case of an encyclopedia article, for example, it might look like this

R. Paschotta, article on 'optical heterodyne detection' in the RP Photonics Encyclopedia, https://doi.org/10.61835/79k, retrieved 2023-11-16

In an online publication, both the article title and the name of the encyclopedia should be hyperlinked – preferably using the DOI link found in the box directly below the article heading.

You can find more details on the citing encyclopedia articles page, which is also accessible from the boxes below the article headings. Another nice thing you will find there are the new citation tools: you can easily retrieve the structured citation information to import it into a citation database, e.g. based on EndNote or BibTex.

This article is a posting of the Photonics Spotlight, authored by Dr. Rüdiger Paschotta. You may link to this page and cite it, because its location is permanent. See also the RP Photonics Encyclopedia.

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