A DOI is an online reference assigned to a digital resource (e.g. an article in a journal or research data) to give it a unique and permanent reference on the Internet. The DOIs are permanently connected to the digital resource – regardless of changes on websites or servers being shut down (in this case a DOI is simply rerouted to a new URL). The use of DOIs, for example, prevents the occurrence of dead links when publishers change the web address of a server. Among all the different ways to reference digital objects on the Internet permanently, DOIs have become the leading system when publishing text and data.