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Advanced Search Strategies: More About Boolean Operators

Tips for using advanced search strategies in library databases


One Search Term

This diagram shows how a keyword search using a single search term or word finds a subset of the total number of records in the index. You may wish to equate this with selecting a subset of the students in your class, just those who are wearing hats.

AND Operator

Generally, you want to start by finding a pool of 50 to 100 records, from which you will select those most relevant to your topic. If you find more than 100 records with a search, chances are that many of them are not relevant to your topic. Reducing the number of results should produce a list that is both more useful and more manageable. A shorter list will also save you time. One way to make your list of results shorter is to use the Boolean operator "AND."

A search using the AND operator may be written out like this: hats AND hoodies

Note that the AND operator is typed in all capital letters.

The diagram shows two words or terms combined using the "and" operator to find only those records containing both terms. It will produce a shorter result list than a single term search. The order of the words does not matter. In our class example, it would find only those students wearing both hats and hoodies.

OR Operator

If you find fewer than 100 records, you may want to increase the number of results. One reason for this is that you may not be searching using the same words that appear in the record, so there may be more pertinent information that you will find by doing a new search using synonyms or related terms. One way to do this is using the Boolean operator "or."

This diagram shows how combining two words or terms with the "or" operator finds those records containing one or both terms. In our class example, it would find those students wearing either blue or green, or both colors.

The "or" operator is often used to look for synonyms, near synonyms, spelling variations or different facets of a topic.

For example, if this picture were your topic you would start by brainstorming all the words you can think of to describe it:


For example: 

All the words you came up with are possible search terms, and most records will only contain one or two of them. Pick a few of the words, then combine them with "or" to do a broad search for her:

woman OR lady OR female

NOT Operator

Use the Boolean operator "not" to reduce the number of search results and eliminate those containing the specified word or phrase.

blue NOT hat

greek NOT fraternity

apples NOT oranges

Some databases use "and not" or "or not" so remember to check the search tips.