What will happen to the number of returns you get if you use the not boolean operator in a search?

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:

woman

For example:  woman female lady feminine girl

gal

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.

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Truncation increases the number of search results you retrieve by finding any variations of a root word. Most databases use an asterisk (*) to truncate words.

Be careful with truncation. In the example below, the search would also retrieve results with words like gamble and gamete.

Adapted from design by UC San Diego Library.

Boolean operators are the words "AND", "OR" and "NOT".  When used in library databases (typed between your keywords) they can make each search more precise - and save you time!   See the steps below (or if you prefer, here is a short video).

AND narrows a search by telling the database that ALL keywords used must be found in an article in order for it to appear in your results list. Search for two or more concepts that interest you by combining descriptive keywords with AND. 

For instance, if you're interested in reading articles about how young people feel about politics, you can search for youth AND politics.  All articles in your results will include both keywords.  Often, databases will allow you to specify where in the article you want those keywords to appear (title, abstract, full text, etc.).

OR broadens a search by telling the database that any of the words it connects are acceptable. This is particularly helpful when you are searching for synonyms, such as “death penalty” OR “capital punishment.” 

So, if you type in death penalty OR capital punishment, your results will include articles with either term, but not necessarily both.

NOT narrows your search by telling the database to eliminate all terms that follow it from your search results. This can be useful when:

• you are interested in a very specific aspect of a topic (letting you weed out the issues that you're not planning to write about)
• when you want to exclude a certain type of article (book reviews, for instance, aren't typically helpful when writing a college-level paper)

Use NOT with caution as good items can be eliminated from the results retrieved. 

In the example below, searching for sex education NOT abstinence-only will return articles on sex ed, but not those dealing with abstinence-only approaches.

Boolean Operators are specific words used to combine concepts or keywords to improve the chances of finding relevant information. The most commonly used Boolean Operators are AND, OR, and NOT.

• Using AND narrows the search and decreases the number of results
• Using OR searches a broader range of keywords and increases the number of results
• Using NOT excludes information not required and reduces the number of results

Brackets are used to define the order in which the concepts are processed. Use brackets when using Boolean Operators such as ‘(art AND therapy) NOT children’ so that the database will only look for articles about art and therapy but exclude those that mention children.

Now test your understanding in the next example by identifying how the results would appear and then clicking on the answer symbol to check your answer.

Boolean Operators and combining concepts

Boolean logic uses the terms AND, OR and NOT to combine concepts. Ithaca College Library in the US uses ice cream to illustrate how Boolean Operators work [7] .

In database searching ‘OR’ expands a search by broadening the set. It is often used to combine synonyms or like concepts.

Strawberry OR chocolate OR vanilla = an ice cream lover with global tastes

e.g. A textword search for information about teenagers should include the words most commonly used: adolescents OR adolescence OR teens OR teenagers OR young adults

In database searching ‘AND’ narrows a search. It is often used for linking together different concepts.

Strawberry AND chocolate AND vanilla = an ice cream lover who only eats ice cream which combines 3 flavours at the same time (i.e. Neapolitan ripple).

e.g. The following statement, students AND behavior will only retrieve records in which the words ‘students’ and ‘behavior’ appear in the same document.

In database searching, ‘NOT’ is used to get rid of an unwanted concept.

(Strawberry OR vanilla) NOT chocolate = an ice cream lover allergic to chocolate.

e.g. If you were interested in information on university students but not high school students, you could search (university students) NOT (high school).

But BEWARE! – this will exclude articles which discuss both types of students.

Combining operators

You can combine sets in a variety of ways using combinations of Boolean Operators. When writing out the sets, parentheses are important because they define the order in which the concepts are processed in the same way as brackets and parentheses are used in mathematical equations. ‘AND’ takes priority and is processed first - unless you use brackets to group concepts. Look at the examples below.

e.g. To find information on the incidence of salmonella food poisoning caused by hamburgers, with or without eggs:

• salmonella AND hamburgers AND eggs = food poisoning caused by both
• (hamburgers OR eggs) AND salmonella = food poisoning caused by either
• hamburgers OR eggs AND salmonella = food poisoning caused by eggs, as well as hamburgers which have salmonella and which don’t (the ‘AND’ is processed first).
• (hamburgers AND salmonella) NOT eggs = only food poisoning caused by hamburgers, removing the confounding effect of having eggs at the same time

The intersection of the circles indicates women who have breast cancer and who also smoke:
women AND breast cancer AND smoking

To find the women who have breast cancer but who don’t smoke, the search statement would be:
(women AND breast cancer) NOT smokers

This describes the intersection between the blue and pink circles excluding the overlap with the yellow circle.

Be careful using 'NOT' - it is very easy to exclude information which is relevant.