More and more scholarly publications appear in electronic format, not only in printed format. It is advisable when referencing to electronic sources to include the same elements that are used with printed sources, and to add details about the electronic source that are necessary to locate it. Examples of these elements are DOI's and URL's.
The DOI (Digital Object Identifier) plays an important part in the referencing system of APA. The DOI is a unique and permanent alphanumeric string that is assigned to many scholarly articles and other publication types. It is permanent and keeps working even if the location of a publication on the Internet is changed.
The DOI number looks as follows:
This link leads you to the electronic version of the publication.
In journal articles you find the DOI on the first page, often near the copyright notice (in the top right or at the bottom of the first page). The DOI is presented in both the electronic and the printed version of an article.
In databases which refer to journal articles (f.i. Web of Science, PubMed, PsycINFO) you often find the DOI included in the records.
If you have a DOI, use it when referencing even if you have used the printed version of an article. .
If you do not have a DOI, but the publication is available online use the URL (Uniform Resource Locator) of the publication.
Often you find different versions of journal articles on the Internet. Many journals put a prepublication version on the Internet before the article is officially published. If possible, refer to the definitive version of a publication.
If you need more than one line for a DOI or URL, break the DOI or URL before a period or slash and make sure you do not create a hyphen. Do not add a period after the DOI or URL.
When a DOI or URL is long or complex, you may use shortDOIs or shortened URLs if desired.