Boolean operators define the relationship between search terms.
Here is a series of Venn diagrams to show you how the Boolean operators limit or expand searches.
AND = searches for sources that contain both words; example:
survival AND mortality
OR = searches for sources that contain either word (the first word, the second word, or both words); example:
survival OR mortality
NOT = searches for sources that contain the word before the Boolean NOT, but not the word after the NOT; example:
survival NOT mortality
Terminology search strategies focus on the words that you use in your searches. These strategies are very precise.
Keyword searching is a form of search strategy that most people know. When you type a word in a search box and click "Search" without adding any additional information, that's a keyword search.
Phrase searching is similar to keyword searching, but instead of searching for one word, you're searching for a phrase. Phrases are surrounded by quotation marks to keep the words of the phrase together. Otherwise, the search interface will usually search for the words anywhere, not necessarily together. For example, searching for "influenza vaccine" - including the quotation marks- will search for the phrase together, instead of the word influenza in one location and the word vaccine in a different location.
Proximity searching locates words within a specific distance from each other. The number in the search phrase tells the search interface how many words away from each other the search terms can be. This allows a limited number of other words to be placed between the search terms, providing more possibilities for search retrieval within a limited scope.
Here’s the order of terminology search types based on restrictions placed upon the search.
Wildcard searching replaces the wildcard character with any other character or characters, or sometimes no characters. Typical wildcard characters include the asterisk (*), pound sign or hashtag (#), or question mark (?). Some databases accept multiple wildcard characters. Others only accept one or two. Be sure to check the database's "Help" page to find out this information.
Truncation searching is a specific type of wildcard search that replaces the wildcard character with any other character or series of characters at the end of the word. Truncation characters are almost always asterisks (*).
Field terms are words or phrases located in an item's record according to a specific type, or field. To search according to field term, select the field from the drop-down menu next to the search box.
These are the main field search limiters that will appear in most search systems. Many databases will have additional field terms, such as geographic locations or other numeric codes. Explore the drop-down menus to find out what’s available.
Site extension limiters limit a search to a specified domain (or domains, if you limit to more than one). Because this search strategy is only limiting the domain result, it can only be used with web searches. There are a couple of different ways to limit to a site extension.
To apply more than one site extension limiter, add both the connecting Boolean operator OR and the limiter by hand in the search bar.
"mortality rates" site:.edu OR site:.gov
The example above searches for the phrase "mortality rates" in both .edu and .gov sites. Be sure to use the OR Boolean operator because you want either type of site. (If you get confused about whether to use AND or OR, remember that websites can't have more than one domain. They can't be both .edu and .gov at the same time.)