Boolean Operators: AND, OR, and NOT
AND, OR, and NOT
Now that you've come up with a list of keywords that might describe the information or ideas that you're hoping to find in the library databases, you need to think about how you will combine these terms in order for the databases to be able to understand what you want. Databases use something called Boolean logic, which basically means that you need to use specific words to combine your keywords in order to get the best results. AND, OR, and NOT are the words most commonly used to combine keywords--they are called Boolean operators. Using Boolean operators can help you create a very efficient search.
Using AND to combine keywords will narrow your search, and make sure that the database only retrieves articles that include ALL of the terms that you combine with AND.
The Boolean operator AND tells the searching software to retrieve only those records which contain both of the specified terms. For example, to go back to the concepts that we had identified earlier: What are the effects of raising the minimum wage on the economy? OR By what amount should the minimum wage be raised?
From these keywords, you can create a basic search: "minimum wage" AND increase
Using OR to combine keywords will expand your search. OR is most often used to combine synonyms. You want to think of synonyms for each of the keywords that you've come up with so that you don't miss any articles that might be relevant, but that might use a different word or term. Using OR will tell the database to retrieve articles with any ONE of the terms you've entered. For example, if you would accept either increase or raise, you can create this search: raise or increase
Using NOT to combine keywords will narrow your search. Basically, NOT allows you to exclude a particular idea or term from your search. Often, it is helpful to use NOT toward the end of your research process, because you don't want to exclude too many things too early. For example, you may wish to search for information on the minimum wage but exclude information on the living wage. Here is a search that you can try: "minimum wage" NOT "living wage"
After you've read through this section, and looked at the examples, go back to your list of keywords. Create a basic search statement using those keywords, using the AND and OR operators. Using the examples from above, a sample search statement might look something like this: "minimum wage" AND (raise or increase). Once you see what you retrieve from that search then you can consider whether to add in a NOT statement.