Break Down Your Topic into Concepts
Databases have difficulty searching for sentences and plain language text. Search by using the most important terms in your topic. DO NOT ask "Should marijuana be legalized in all of the United States of America?" Many of the words in this sentence would confuse a database search. By ignoring articles, pronouns, prepositions, and other unimportant words, you will be left with the key words to use in your search. Begin by crossing out the unimportant words and focusing on the key concept terms:
Should marijuana be legalized in all of the United States of America?
When searching for articles on this topic in a database, simply use the terms:
Brainstorm for Synonyms Related to Your Concepts
Now that you've broken down your research question into the specific concepts, think about all the other words an author might use to talk about these concepts. In other words, find synonyms or related words for each concept term/phrase. Hint: use a thesaurus if you get stuck.
marijuana: maybe pot, but probably stick with marijuana
United States: US, America
legalize: legalization, legal, decriminalize
(This information is from : http://libguides.sjfc.edu/content.php?pid=346475&sid=2905537)