Boolean Operators (AND, NOT, OR)
Boolean Operators are a set of fixed words, AND, NOT, and OR, that are used in most search engines. These words have specific functions in the search process.
The easiest to describe is OR. When OR, in all caps, is placed between two word in a query, the engine will look for any occurrence of either word. OR expands the results list. The search engine is looking for either topic. In a way it is committing 2 searches, but putting the results in one list.
AND, on the other hand, is used to narrow the results. When AND is placed between both words the search engine is looking for all occurrences where BOTH terms are present in the same page. So, if a website only has only one of the terms, it will not be listed in the results page. AND narrows the results to have BOTH terms present.
The other fixed term is NOT. NOT simply removes pages that have that term. So, the search engine will find all occurrences of the term, but then remove those that have the second term, the term listed after NOT.
In most of our databases we recommend using the "Advanced Search" function. On those pages, the multiple search boxes are often connected by Boolean operator dropdown menus (AND, NOT, OR).
In this diagram the entire area of both circles, the blue area, represents all items containing either A or B. It represents A OR B. Even the area of overlap. That is also A OR B.
In this diagram the area in the middle, the purple, is the intersection of A and B. It represents A AND B.
In this diagram the area on the left, the yellow, is the results all A, but not B. It represents A NOT B. The orange center represents A AND B. The red area represents B NOT A