BOOLEAN SEARCHES

Boolean Operators

1. In conducting a search, you may also use Boolean operators (AND, NOT, OR, XOR).
2. The Boolean operators allow you to refine your queries to focus on more specific or more general information than may be found with a single word or phrase search.
3. Boolean connectors require a word or phrase on either side of the operator. For example, negligent or intentional is a valid query, but or intentional is not.
4. There are four Boolean operators: And, Or, Not, Exclusive Or. See Operator Precedence for a discussion of the precedence (order of execution) of these operators and how to override the precedence.

Boolean operator: And

1. Use the And operator to search for multiple words in the same record (this is same as the multiple word search described in Simple Queries).
2. The And operator may be specified any one of three ways: a single space between words, the ampersand &, or the word and.

Boolean Operator: Or

1. Use the Or operator to search for multiple words in the infobase (the words may or may not be in the same record).
2. The Or operator may be specified by the word or.

Boolean Operator: Not

1. Use the Not operator to search for records which do not contain a particular term or set of terms. Not is actually a unary operator (it can be used by itself), but it is often used in between two terms (find records which contain A but not B).
2. Generally, the best way to think of the Not operator when used between two terms (A not B) is "find records with A and find records without B" (A and not B).
3. The Not operator may be specified one of two ways: the caret ^ or the word not. (The caret ^ is usually above the number 6 on the keyboard)

Boolean Operator: XOr (Exclusive Or)

1. Use the XOr operator to search for records which contain one of two words but not both.
2. The XOr operator may be specified one of two ways: the tilde ~ or the term xor.

Operator Precedence

1. The query operators have a precedence order. That is, when two more operators are used in a query, the results of one operator will be evaluated before another operator. Understanding the precedence and how to override the precedence can assist you in finding the information you need.
2. The operator precedence is: Not, Or, XOr, And
3. If the same operators are used in a query (for example, if Or appears twice in a query), the operators are evaluated from left-to-right.
4. For example, consider the following query: dog or cat and mouse not cheese
5. This query is evaluated in the following order:
   1. not cheese (records which do not contain cheese)
   2. dog or cat (records which contain either dog or cat)
   3. and mouse (and all records in the identified subset which contain mouse).
6. These rules allow you to create powerful queries; however, they can also be confusing. To ensure the correct terms are combined with the correct operators, use parentheses around the terms and operators.
7. For example, the following queries all produce different results:
   dog and (cat or mouse) not cheese
   dog and cat or (mouse not cheese)
   (dog and cat) or (mouse not cheese)
8. The following query is the same as the first query in the above list, but is more explicit:
   (dog and (cat or mouse)) not cheese
   

Updated January 2000
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