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Combining keywords

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Boolean operators

To search an electronic database, you will usually need to combine your keywords and phrases. This approach will allow you to find just those references which relate to your particular topic.

Keywords are usually combined using Boolean operators. These are connectors which determine the relationship between different keywords.

Boolean operators can be employed when you:

  • use an online Library catalogue;
  • search the World Wide Web; and 
  • use an electronic journal index.

Introduction to Boolean Operators

View this short clip (3.03min) for an overview and some tips on how to use AND, OR and NOT.

The basic Boolean operators

The three main Boolean operators are AND, OR and NOT.

AND

The AND operator narrows your search because it finds records which contain all of the terms you want to combine. This is the most common operator used because it allows your search to be quite specific.

Fig 1 The AND operator

For example, greenhouse effect AND Antarctica will find just those records which include both concepts (Fig 1).

Note that you can add a whole string of keywords together using the AND operator: greenhouse AND Antarctica AND seawater AND temperature.

OR

The OR operator looks for any items which contain either or both of the terms you want. This will broaden your search and is particularly useful for spelling variations, plurals and alternative terms.

Fig 2 The OR operator

For example, e-commerce OR electronic commerce will find records which mention either or both terms (Fig 2).

NOT

Using NOT allows you to exclude terms, narrowing your search. Records are retrieved which have one term, but not the other.

Fig 3 The NOT operator

For example, vegetables NOT carrots will find items with the term vegetables but will exclude any containing the term carrots (Fig 3).

A word of warning

Sometimes electronic search tools use + or – instead of the operators AND and NOT, so check the online Help of the particular search tool you are using for the correct method of employing Boolean searching.

It's also a good idea to check in the online Help to see how the designers have decided to use Boolean concepts. Sometimes the software inserts a hidden AND between two keywords.

Truncation

Searches can also be broadened by using truncation. Truncation allows you to search for words with varying endings. An * is generally the symbol for this, but alternatives are !, #, and $. Look in the online Help of the search tool you are using to find the correct symbol.

nurs* will find records containing the words nurse, nurses, nursing, nursery, nurseries.

A word of caution here: you can get unexpected results such as garden nurseries or references to child care.

Wildcards

Wildcards (generally a ?) replace single characters and are great for plurals and spelling variations.

behavio?r finds records containing behavior (US spelling) or behaviour (British/Australian spelling).

organi?ation* will result in items containing organisation, organization, organisations, organizations, organisational and organizational.

Summary

This page provides an introduction to the concept of Boolean operators. It discusses:

  • the three basic Boolean operators (AND, OR, NOT);
  • truncation; and 
  • wildcards.

Boolean operators are vital tools for searching all sorts of electronic information resources. Let's go to discuss how you can choose the right tools to help you in your search.

Link to page with self-test questionsSelf-test

Try these quick self-test questions to assess what you have learnt from this module.