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Boolean operators

Boolean operators are used to combine keywords when searching databases. Some databases' search screens will include a drop down box where you can pick your operator, e.g.

Others will expect you to type in your operators, e.g.

Boolean operator - AND

AND is used to bring together concepts:

'public opinion' AND 'US Government' AND 'foreign policy'

 

Combining keywords (concepts) with the operator AND will narrow your search results to documents that include both keywords (concepts).

AND - Example 1

'foreign policy' AND 'US Government'

In our example the keywords are expressed as two phrases. This search strategy will limit your search results to those items that contain both phrases.

The coloured circles below illustrate the retrieval pattern for the AND operator. Each circle represents a set of documents that contain a keyword. One circle represents a set of documents containing the keyword/phrase 'US Government' the second the set of documents containing the keyword 'foreign policy'. Bringing together these keywords with AND results in the single set of documents outlined in red.

Illustration of the AND operator

AND - Example 2

If you used the search strategy 'foreign policy' AND 'US Government' to search the table/database of 5 article titles below all the ticked titles would be returned by the search:

United States discusses foreign policy with Cuba.
US government decides that foreign policy has to be reviewed. Tick
Foreign policy to be decided.  
Foreign policy and financing by US government to be decided. Tick
US government to give billions to developing countries.

Boolean operator - OR

Combining concepts with the operator OR will expand your search e.g. 'onions' OR 'carrots'. OR is also used to bring together alternative ways of expressing a concept, e.g. 'US Government' OR 'American Government' OR 'White House'.

OR - Example 1

'US Government' OR 'American Government'

This search strategy will retrieve all items containing 'US Government', all items containing 'American Government' and all containing both phrases.

The coloured circles below illustrate the retrieval pattern for the OR operator. Each circle represents a set of documents that contain a keyword. One circle represents a set of documents containing the keyword 'US Government' and the other the set of documents containing the keyword 'American Government'. Bringing together these keywords with OR results in the single set of documents outlined in red.

'US Government' OR 'American Government'

Illustration of the OR operator

OR - Example 2

If you used the search strategy 'Foreign policy' OR 'US Government' to search the table/database of 5 article titles below, all the ticked titles would be returned by the search:

United States discusses foreign policy with Cuba. Tick
US government decides that foreign policy has to be reviewed. Tick
Foreign policy to be decided. Tick
Foreign policy and financing by US government to be decided. Tick
US government to give billions to developing countries. Tick

Boolean operator - NOT

Combining keywords with the operator NOT will exclude words/phrases and narrow your search.

NOT - Example 1

'foreign policy' NOT 'US Government'

This search strategy will exclude the phrase 'US Government' and only retrieve records containing the phrase 'foreign policy'.

The coloured circles below illustrate the retrieval pattern for the NOT operator. Each circle represents a set of documents that contain a keyword. The first circle represents a set of documents containing the keyword 'Foreign policy' and the other the set of documents containing the keyword 'US Government'. Bringing together these keywords with NOT results in the single set of documents outlined in red.

Illustration of the NOT operator

NOT - Example 2

If you used this search strategy: 'Foreign policy' NOT 'US Government' to search our database of 5 article titles the ticked titles would be returned:

United States discusses foreign policy with Cuba. Tick
US government decides that foreign policy has to be reviewed.  
Foreign policy to be decided. Tick
Foreign policy and financing by US government to be decided.  
US government to give billions to developing countries.