A DOI can be verified as correct either by using http://crossref.org or by adding the prefix http://dx.doi.org/ to the DOI to do a web search.
In the example to the right, the DOI is 10.5330/PSC.n.2011-14.271. In order to verify this DOI, you can add http://dx.doi.org to the beginning, so you would be searching for http://dx.doi.org/10.5330/PSC.n.2011-14.271.
According to http://www.crossref.org, "(a) Digital Object Identifier (DOI), is a unique string created to identify a piece of intellectual property in an online environment." DOIs are attached to articles and papers found in databases and many other publications.
Here is an example of a DOI for an article found on PsychArticles from EBSCO:
In general APA states the following for journal articles found online:
Article From a Database