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Search strings

Constructing a search string: Boolean operators

What is Boolean searching?

Most searches will return too many or too few records. It takes a long time to look at hundreds of records. By putting a little effort into constructing search strings (what you type into the search box) you can save a lot of time. The database can do a lot of work for you if you know how to add a little sophistication to your search strings.

To do this with databases you need to know about the Boolean system. By the use of a few simple linking words, called operators, you can make your searches much more precise.

Narrowing Searches - the AND, AND NOT Operators

If your search returns too many records, you can narrow your search by adding more search terms. To ensure all the records your search finds contain all the search terms, link them with the and operator. For example, let's say you were interested in only red cars. To avoid having to sift through records on blue cars, green cars and so on, you would use the following search string:

red and cars

If you do not wish to see records containing a certain term, you can exclude these by using the and not operator. If you were interested in cars of any colour as long as they are not blue, you would use the following search string:

cars and not blue

Be careful when using this, you may miss records that contain useful information because you have excluded too many records. It is not recommended that you use this operator for your first search attempt, just add it to your search string if you are getting too many irrelevant results and then check it isn't excluding too many documents. Generally, adding further terms with the and operator is a safer way of refining your search.

With some search engines you will need to use not rather than and not, check the help pages if you are not sure.

Broadening Searches - the OR operator

If your search returns few or no results, you might have more success if you can think of alternative search terms. These can include:

  • other terms related to your topic
  • synonyms (words with the same meaning)
  • different word endings (for example singular and plural forms)
  • different spellings (for example UK versus US spelling)

To search for records that return one or more of your search terms, link them together with the or operator. For example, cars are also known as automobiles and so to catch as many relevant records in your search as possible, you would use:

cars or automobiles
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