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a. Logical OR (inclusive)


The logical OR is the class union operator. The result of the logical OR between two classes is the class obtained by merging the two classes retaining common elements (if any), only once. 

Thus, if A and B are two terms representing the two classes of documents indexed with terms A and B respectively, the logical OR between these two classes is the class of documents indexed with term A or term B or both. The logical OR therefore is used to broaden the scope of the search and will in general increase the number of hits. The symbol used to indicate the logical OR operation is the plus sign ( +). 

Thus, for example, to retrieve documents about food or malnutrition, or with the word "Africa" in the title, the logical OR operators could be used as follows: 

"TI=AFRICA" + "D=FOOD" + "D=MALNUTRITION" 

Note that the order in which the three terms are given is irrelevant. 

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