Some databases will automatically generate a citation in MLA and other formats. Others will only provide the basic information, and it's up to you to do the formatting. Look for links like "Cite" or "How to cite" within the databases and on article pages. Also check the top and bottom of the page or article for citation info.
Warning: Most of the citations in databases, web services, etc., are produced automatically using a computer algorithm. That means that if the data is incorrect, the resulting citation is incorrect. You have the final responsibility of checking that the citation is fully correct using the guidelines provided by your professor (or publisher).
