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Proteomics in Plant Biology: Research Guide: Databases

For MBBE seminar course Spring 2017

Boolean Operators

Boolean Operators link concepts and are used to broaden or narrow your search. Briefly, here's how they work:

AND - finds results with your all search terms.  AND narrows your search.

OR - finds results with any of your search terms.  OR broadens your search.

NOT - finds results with only one of your search terms.  NOT narrows your search.

Use the tabs along the top to see more information about Boolean Operators and how to use them.

Free Databases

Using Parentheses

You can use parentheses to build a search with a combination of Boolean Operators.

Take a look at the illustrations below - the search terms and Boolean Operators are identical, but the parentheses create two very different searches.

Using parentheses in your Boolean search, is a lot like using them in arithmetic - the search inside the parentheses is done first.

Lets take a closer look.


The blue area in the first illustration represents the results that would be returned for the search (Cetacean OR Whale) AND Pacific, which yields 633 results and gives us articles with the following combinations:

Cetacean, Pacific
Whale, Pacific
Cetacean, Whale, Pacific

Note that Cetacean and Whale may or may not be present, but Pacific will appear in every search result.  This is because Cetacean and Whale are linked with OR while Pacific is added to the search with AND.



The blue area in the second illustration represents the results that would be returned for the search Cetacean OR (Whale AND Pacific), which yields 1718 results and gives us articles with the following combinations:

Whale, Pacific
Whale, Pacific, Cetacean

Note that Whale and Pacific must always appear together, or not at all, while Cetacean may be the only term present.  This is because Whale and Pacific are linked with AND and Cetacean is added to the search with OR.



When the same search is run with no parentheses - Cetacean OR Whale AND Pacific - we get the same search results as Cetacean OR (Whale AND Pacific). This is because of search precedence which is discussed to the right.

Search Precedence

Databases are programmed to prioritize Boolean Operators.  This is often called "search precedence" and it influences how your search is performed. 

For instance, most databases give AND precedence over OR, meaning terms linked with AND will be searched before those linked with OR, no matter the order they appear in your search. 

In any database, using parentheses will override the search precedence.