Boolean queries involve the following special operator expressions:

In these queries, x and y can be either simple terms or expressions, which together form a complex Boolean expression. Parentheses are used to clarify the syntax of complicated queries, such as

x and (y or z)

Some search engines conceal this syntax by providing several Boolean fields for input:

Another approach is to simplify the Boolean syntax and limit the expressive power to make it easier for end-users to master. This simple Boolean syntax typically has just two operators:

These simple operators can approximate more complex full Boolean syntax. For example, x AND y could be entered as +x +y. x AND NOT y could be entered as +x -y. x AND (y OR z) could be entered as +x y z, assuming the search engine defaults to a Boolean OR of terms. The behavior may not be exactly the same, and depends greatly on the search engine, but this syntax is clearly a simple and effective alternative to full Boolean expressions.

ATG Search supports both forms of Boolean syntax and has extended some of the syntax to adapt to its two-level index. The ATG Search query operators are described in detail in the User-Entered Query Operators chapter.

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