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A general guide to resources in the field of biology

Combine Your Searches

Once you have identified some search terms, you will need to combine them in a way that the search tool (e.g. library catalogue, database, Internet search engine) will understand. Most search tools use connector words like AND, OR and NOT. These are Boolean operators.


The AND operator helps to narrow searches. 

An easy way to remember this is to think of it this way: AND = narrow

Most search engines (Google, Google Scholar) and the Library's Summon "Search Everything" tool, automatically place an invisible AND connector between your keywords, so that you don't have to type it in.  They use an implied AND.  However, many of the Library's more specialized research databases will require you to type the AND into the search box when you enter your terms.  

(e.g.) diagnostics AND cancer

This will tell the search tool to find records that contain both of these words.  It will not find records that contain only one of these words.

If you find you are still getting too many results in your searches, consider narrowing your search further by adding another search term using AND.  For example:

diagnostics AND cancer AND AI

Variations on the AND operator:  AND, and, &, +


Or helps to expand or broaden search results.

An easy way to remember this is to think of it this way: OR = broaden

It is used when you want to find results that contain either term; you are not necessarily wanting both terms to be represented.  It can be very useful when you want to search for synonyms, related terms, or variations in spelling.

(e.g.) AI OR machine learning OR artificial intelligence

Variations of the OR operator: OR, or, /


You can use NOT to eliminate concepts from your search results to avoid irrelevant results.  For example, if you are looking for information on coaching in the workplace but are not interested in athletic coaching, you could do this:

coaching NOT athletics

The search tool would return results containing the word coaching but would eliminate any results containing the word athletics.

Note:  While NOT can be a useful tool, it should be used with caution - because the database you are searching is only looking for the appearance of the word, but does not understand context, using NOT can sometimes eliminate very relevant results.  For example, with the above search, let's say there is an article in the database with the title: Not Just for Athletics: A Review of the Benefits of Coaching in the Workplace -- This sounds like an excellent article for our sample topic but, if we used the above search (coaching NOT athletics), it would not be displayed in our results because it contains the word athletics and we told the database not to bring back results containing that word.

In general, it's best to avoid using NOT unless absolutely necessary.  It's better to try using AND to narrow your search results down to a manageable number, then use your judgement to eliminate irrelevant results.

Combining AND, OR

You can express complex search ideas by using both AND and OR.  For example, you can combine the above searches into one "search string" as follows:

diagnostics AND cancer AND AI

diagnostics AND cancer AND (AI OR machine learning OR artificial intelligence)

The results of this search must contain:
the term: change
one of the terms: employee, staff, personnel

Important! You do need to use brackets around terms that use OR, to ensure they are being searched together.

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