Boolean Searching

Boolean operators AND, OR, and NOT can be used to combine search terms when you need to expand or narrow a search. Parentheses ( ) are used to specify the order in which terms will be combined.

AND

AND retrieves only records that contain all search terms, so its use narrows the search.

If you enter:	You retrieve:
railroad AND subway	only records containing both railroad and subway
airplane AND airport AND terminal	only records containing all three search terms-- airplane, airport , and terminal

OR

OR retrieves all records that contain one or more of the search terms, so its use expands the search.

If you enter:	You retrieve:
railroad OR subway	records containing railroad, records containing subway, and records containing both
airplane OR airport OR terminal	records containing airplane, records containing airport, records containing terminal, and records containing any combination of two or all three search terms

NOT

NOT excludes records that include the search term or a group of search terms.

If you enter:	You retrieve:
railroad NOT subway	records containing railroad which do not include the search term subway
airplane AND airport NOT terminal	records that contain both airplane and airport but do not include any reference to terminal

Parentheses (nesting)

Group terms in parentheses to specify the order in which they will be combined. Without parentheses, terms will be combined in left-to-right order. For example, railroad and subway or Amtrak can be combined with parentheses to give you two distinctly different sets of results.

If you enter:	You retrieve:
railroad AND subway OR Amtrak	records containing both railraod and subway , then records containing Amtrak whether or not they contain railroad or subway
(railroad AND subway) OR Amtrak	the same results as above
railroad AND (subway OR Amtrak)	records containing either subway or Amtrak or both; it then searches that set of records for records that contain railroad so that all records contain either subway and railroad or Amtrak and railroad  or subway and Amtrak and railroad

Processing Rules

• Process AND, OR, or NOT in left-to-right order unless ( ) are used .
• Process AND, OR, or NOT in ( ) first.
• If there is more than one ( ) in a search, process them in left-to-right order.
• If there are ( ) within ( ), process them from innermost to outermost.
• Process two words with only a space between them as if AND was between them and they were enclosed in ( ). For example, hybrid car OR electric vehicle is processed as (hybrid AND car) OR (electric AND vehicle).
• On the Advanced search screen, process AND, OR, or NOT typed in a search box as if they were enclosed in ( ). For example, if you type car AND safety in the first search box and air AND bag in the second search box, it is processesed as (car AND safety) AND (air AND bag).

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Related topics:

• New Search / Simple Search
• Advanced Search
• Phrase Searching
• Truncation, Wildcards, and Word Stemming
• Adjacent terms (proximity)
• Stopwords