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Using the Cited By Feature of Crossref

Posted on 2023-11-20 as part of the Photonics Spotlight (available as e-mail newsletter!)

Permanent link: https://www.rp-photonics.com/spotlight_2023_11_20.html

Author: Dr. Rüdiger Paschotta, RP Photonics AG, RP Photonics AG

Abstract: Being a member of Crossref, RP Photonics used the opportunity to implement the feature to search for publications citing a specific paper. This can be useful in various ways.

Dr. Rüdiger Paschotta

It is unusual for me to publish a Spotlight article a few days after the last one, but there is another interesting news item that I was keen to present straight away. Last time, I reported that RP Photonics had become a member of Crossref, which allowed me to implement another really useful feature called “cited by”. Behind every bibliography entry (see for example the article on adaptive optics) that has a DOI (which is the case for the vast majority of references), there is now a “cited by” button. This allows you to have Crossref search for other papers that cite that particular paper. Another nice extension of the functionality of the RP Photonics Encyclopedia!


You can think of several applications for this feature, especially in the context of scientific research; some examples are:

  • Tracking the impact of research: By seeing who has cited their own work or that of others, researchers can gauge the impact and reach of a publication within the academic community. Frequent citations indicate that the work is influential in its field. Such information can also be useful in job or grant applications.
  • Assess the quality and reliability of research: By reading the publications that cite a particular paper, one can see whether others have positively acknowledged various aspects of it, or expressed doubts and criticisms about the claims made. Credibility and significance can then be better assessed.
  • Find related newer research: The “cited by” feature helps researchers discover related studies or papers that they might not have easily found otherwise. This helps to get a more complete overview of a research area. This is especially important when conducting literature reviews or meta-analyses.
  • Networking and collaboration opportunities: Researchers can identify potential collaborators through the “cited by” feature. By examining who has cited their work, researchers can find others working in similar areas, potentially leading to collaboration opportunities.

Technical Remarks

Crossref coordinates a large collaborative effort. Its goal is not only to store the bibliographic information provided by all its members, but also to identify and exploit the relationships between these works – especially those established by citation. For that reason, Crossref strongly recommends that members not only use the “cited by” feature, but also support it by providing citation data. Therefore, with our data uploads, we now provide information on all cited references for each encyclopedia article. Most of these references contain a DOI, making it very easy for Crossref to identify the work in their database.

Since our encyclopedia articles are not immutable, i.e., references may be added later, we regularly update the information in Crossref.

The technical implementation of the “cite by” feature was a bit tricky in several ways. Here are a few notes:

  • Some JavaScript / jQuery code adds such a button to all references (except those few without a DOI) after loading an article page.
  • Each of these buttons has an event handler that calls a JavaScript function when the button is pressed.
  • In principle, this function could send a query directly to the Crossref server, but we don't go that route because someone could read our script, which would have to contain our secret credentials. Therefore, the secret part is done in a PHP script that can be executed but not downloaded and inspected by users.
  • The PHP script is used in an Ajax call from JavaScript. Since we don't want anyone to abuse it for general “cited by” queries (which Crossref only allows members and their users to do), it is not told the article DOI directly, but rather the article page and reference number, from which it extracts the DOI itself. This method will only work for articles cited by our resource.- The script makes an inquiry to the Crossref server. When receiving its response (in XML format), in returns these results to another JavaScript function. That needs to put together various pieces of information from the XML code and displays the list of found references in a pop-up window, using jQuery UI.
  • As the search at Crossref can take some time (typically, a couple of seconds, sometimes longer), we have some caching of results for 24 hours: data are loaded from a local file when queried again within 24 hours for the same paper.
  • We also must take care not to make that construction vulnerable to cross-site scripting attacks, i.e., the injection of malicious code from somewhere. Normally, we can trust that Crossref will do its best to prevent any members from injecting malicious code into the metadata. However, we want to be double-sure and therefore additionally “sanitize” the inputs.

Based on all this, it is easy to see why not everyone offers this functionality. For many, it would be a costly project to implement, requiring external help. For someone who also develops software, this is not such a big challenge, and in fact it was fun to work out.

We are curious to see how popular this feature will be. The aforementioned PHP script does some logging. But don't worry: As always, we don't collect any personal information, not even your IP address. We just see when someone from a certain country uses “cited by” for a certain article.

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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