Skip to Main Content

Library Search: Boolean searching

Boolean searching

Boolean connectors / operators

You can combine multiple search words together in search databases using connectors.

Connectors can sometimes be referred to as Boolean connectors or Boolean operators.

The most common Boolean connectors are: AND, OR, NOT.

Why use Boolean connectors?

Combining your search words using connectors can improve the relevancy of your results, because connectors cause the search engine or database you are using to search your keywords in a more specific and filtered way.

In many databases, if you don't use a connector between your search words the AND connector automatically applies to your search. For example, the keyword search: Brexit voting Wales would be interpreted as Brexit AND voting AND Wales.


Boolean AND

Using AND between search words will:

- instruct to the database to ensure ALL the search terms are present in the search results

- narrow/ refine your search results


Example search: cats AND dogs. 

Search results: will include both of these words anywhere in the text.


Boolean NOT

Using NOT between search words will:

- eliminate an element from your search

- narrow/ refine your search results


Example search: (voting AND Europe) NOT Italy

Search results: will include both of the words in the bracket where the word "Italy" does not also appear. 

This type connector is good to use when you know what you do NOT want to appear in your search results.


Searching for phrases

Phrase searching 

Most academic databases automatically put a Boolean AND between your search terms if you don't use a connector. This means that the words you search will be present in your search results, but they may not be next to each other. This will have an effect on the number and relevancy of your search results.

If you have two or more words that you want to find next to one another you can easily search for them by placing them in double quotation marks. 

For example:

"European union" 

"family crisis"

Boolean OR

Using OR between your search words will:

- connect two or more similar concepts or keywords together, instructing the database to find ANY of your search terms present in the search results 

- broaden your search results


Example search: cats OR kittens.

Search results: will include either cats, kittens, or both anywhere in the text. 


Example in Library Search

Here is an example of a search using Boolean connectors in Library Search's advanced search option

Here is the same search, but in Library Search's simple search. The separate search groupings are no longer separated by a line (as in advanced search) and so are grouped using brackets instead.


Truncation searching

Searching multiple iterations of the same word at once

Truncation, also called stem searching, is a technique that broadens your search to search various iterations of a word at once, by searching the root word followed by the truncation symbol *. The database will return results that include any ending of that root word.


For example:
searching the root word: child*

finds: child, childs, children, childrens, childhood


Truncation symbols may vary by database; common symbols include: *, !, ?, or #

To use truncation, enter the root of a word and put the truncation symbol at the end.