LOGICAL (BOOLEAN) OPERATORS

All queries are, in essence, a combination of the logical (Boolean) operators And, Or, and Not. The And operator requires that every key word must be present. Searching for "President" and "Clinton," for example, will return documents about Mr. Clinton's presidency. The Or operator, however, requires that only one of the terms be present, so that searching for "President" or "Clinton" will return documents about presidents (any president) and Clinton (any Clinton). Some search engines also enable you to use Not. Searching for "Bill" and "Clinton," but specifying "Not President," will return documents about other aspects of Mr. Clin­ton's life and other Bill Clintons. The way in which you specify the Boolean oper­ators depends on the search engine and is described in its online help.

Figure 5 illustrates the use of the Yahoo search engine to look for infor­mation about Leonardo da Vinci and the Mona Lisa. Figure 5a shows the Search pane of the Explorer bar in which we entered the parameters of the search using the Yahoo engine. Yahoo uses the Boolean And operation by default and returns those documents that contain references to both Leonardo and da Vinci. The results of the search are displayed below the query. The contents of the selected document (the category in this example) are displayed in the right pane.