Lesson 8: Searching with Boolean Logic
Return to Library's Home Page Return to District's Home Page
One of my first classes in the graduate program was a class on research, and it was also the first time I heard the term "Boolean logic." I learned a little bit about it then, but it wasn't until completing lesson 8 of this tutorial that I really started to understand it. The term "Boolean" comes from the name of a British mathematician named George Boole, who lived in the 1800's. He wrote about a system of logic that was developed to help people with finding search results by making their inquiries more precise. It is from his original writings that Boolean logic as it is used today, was developed.
Boolean logic uses three basic operators: AND, OR, and NOT. I will try to explain each of them in more detail:
The Boolean use of "AND" makes the search smaller by only bringing back information that contains every one of the keywords the searcher enters. The more items the searcher enters, the more narrow the subject becomes, because more words have to be included in the results.
Example: diet AND exercise
Example: diet AND exercise AND obesity
The Boolean use of "OR" makes the search larger because using it brings back items that contain any of the keywords entered by the searcher. The more words the searcher enters, the more items will be returned from the search.
Example: greenhouse OR hothouse
Example: greenhouse OR hothouse OR nursery
The Boolean use of "NOT"/"AND NOT" makes the search smaller because it returns only the first keyword but not the second, even if the first work appears in the document as well.
Example: ozarka AND NOT water
Example: bubble AND NOT gum
"Nesting" refers to using parentheses to join more than one search statements together. Parentheses can also be used to separate keywords when the searcher is using more than one operator and three or more keywords.
Example: (HD OR flatscreen) AND (sony OR magnivox)
Another component of Boolean logic is something called "Implied Boolean Operators." This involves the use of the plus sign (+) and the minus sign (-) in the place of the Boolean operators AND and NOT. Putting these signs in front of a word with either force its being included in or excluded from the search. Implied Boolean operators are usually accepted in the basic search option of most search engines.
Example: +"eating disorder" -bulimia
Putting double quotations marks (" ") around two or more words will force them to be searched as a phrase in that exact order.
Example: "red peppers"
There was also an explanation of proximity operators such as NEAR, ADJ, SAME,FBY--these operators are not really part of Boolean logic but they serve a similar use as the Boolean operators.
The use of Boolean logic isn't always easier, and compounding its difficulty is the fact that different search engines handle Boolean operators differently. Like most things having to do with technology, the best way to learn something is by practicing it--over and over. I got a little bit of practice on the assignment for this lesson, in which I had to go to Google and use the advanced search page to try one of the examples given in the tutorial. I actually tried out several of the examples and urge you to do the same.
Lesson 1 Search Engines Lesson 2 Metasearch Engines Lesson 3 Subdirectories Lesson 4 Library Gateways
Lesson 5 Evaluating WebPages Lesson 6 Creating a Search Strategy Lesson 7 Basic Search Tips
Lesson 8 Boolean Logic Lesson 9 Field Searching Lesson 10 Troubleshooting Lesson 11 Clusty Search Engine