Search engines are searchable, browsable indexes of the World Wide Web. Subject Trees are hyperlinked lists of Web sites, hierarchically organized into subject categories and subcategories. Subject Trees are created by people rather than computers. A keyword search can then be used to search within that sub category. Boolean searches Keyword searches utilize a concept known as Boolean logic.
Boolean logic uses a basic syntax made up of search terms and operators.
Using search terms with AND will give you all the hits that contain all of the search terms that you entered. Use AND when you have dissimilar terms and want to narrow your results to fewer, more precise hits. Using search terms with the OR operator will give you all the hits that match at least one of your search terms. This is the default operator for most search engines. Using search terms with NOT will exclude search terms that you do not want included in your results.