A DOI, or digital object identifier, is a unique string of numbers and letters assigned to a source. When the DOI is available, it is the only retrieval information you need to provide for your citation. For example:
Harrison, J. (2008, September). The vagaries of vegetarianism. Ratio, 21(3), 286-299.doi:10.1111/j.1467-9329.2007.00402.x
Journal Articles from a Library Database
These can be cited exactly like the print version. According to the APA Publication Manual, it is not necessary to include the name of the database. However, your instructor may want to know to make it easier to find the article. See Reference List: Electronic Sources (Web Publications) in OWL for more suggestions on this, scroll down to Article from a Database. If in doubt, check with your instructor.
APA Style Website Reference, no author or date
Many webpages do not include author information or the date of publication. If there is no author, the title of the page is listed first, followed by the date in parentheses. If there is no date, use n.d. Do not include the date you accessed the website unless the information is likely to change, as a blog or a wiki.