Same information included as for journal articles (see example above) and a DOI-number. DOI (Digital Object Identifier) is used to uniquely identify an object such as an electronic article. DOI-numbers are permanent, which makes it possible to easily locate articles even if the URL of the article has changed. Articles are assigned DOI-numbers by major academic publishers. If there is no DOI-number you should give the URL-link of the article and in some cases access date (mainly articles that are freely available on the internet). Today the publisher often states how to write the reference.