While databases cannot understand natural language, database searches can be made very precise using Boolean operators. Boolean operators tell databases exactly how you want your search terms combined for the optimal results.
There are only five Boolean operators and all library databases understand them.
The chart below briefly describes their functions.
|Operator||What does it do?||Example|
|""||Holds together the words of a phrase so that the database searches it together instead of separately||"hospital staff"|
|*||Truncates a word so that you get alternate endings||educat* for education, educated, educates, etc.|
|AND||Joins two concepts so that the database knows you want both to be in your search results||dogs AND "service animals"|
|OR with ()||Used to join two or more keywords, usually synonyms or related terms for the same concept, so that the database knows you want either or both of them to be in your search results. Whenever you join keywords with OR, enclose them with parentheses.||(trains OR railroads) AND travel|
|NOT||Used to tell the database that you do not want this keyword or group of keywords in your search results.||nursing NOT (breastfeeding OR lactation)|
While there are only a few operators, they can be combined to create a very sophisticated search for increasingly complex research topics. The video below discusses this in detail as well as how to avoid some common pitfalls of database searching. If you prefer, skip to the text discussion beneath it.
Now let's go into a little more detail about each operator.
Quotation marks tell the database to take the phrase as a whole, and search for the words together, and in order.
Example: Searching wild geese:
The asterisk (*) is a kind of wild card that tells the database to find multiple "endings" of a word.
Example: Searching feminism.
Be careful of truncating too early in the word itself.
AND joins two or more concepts by telling the database that both/all of these keywords must appear in the search results.
Example: Searching for Plato's idea of the good life.
Hint: if your topic is "the X of Y" or "the impact of X on Y," or "X as a Y," or "X in Y," you need to use an AND to join concept X and concept Y.
OR joins two or more keywords for the same concept by telling the database that one or more of them must appear in the search results. It is useful when:
Example: Searching for rabies in mammals
Hint: always put parentheses around groups of keywords joined by OR.
Parentheses tell the database that it cannot just work from left to right - it has to perform certain operations first. That is why you need to put parentheses around groups of keywords joined by OR.
Example: Searching the use of bats and frogs for mosquito control
You can also nest parentheses (put one set inside of another) and the the database will work from inside out.
NOT excludes search results that contain the keyword(s) following it.
Example: Searching for impact of smog on asthma, but you do not want to read about China.
When you might need to use NOT:
It is feasible that you may have such a complex search to perform that you might require the use of all six of the Boolean operators to get optimal search results.
For example, let us say that you are looking for medicines or other medical interventions for seizure disorders other than epilepsy.
This search, using all of the Boolean operators, might look like this:
medic* AND (seizures OR "seizure disorders" OR "convulsive disorders" OR convulsions) NOT epilepsy
Material on this page is adapted from the Research Skills Tutorial by the Librarians at Empire State College has been made available under a Creative Commons Attribution-ShareAlike 4.0 International License.