is language-independent. Applications Compound-term processing allows information-retrieval applications, such as search engines, to perform their matching on the basis of multi-word concepts, rather than on single words in isolation which can be highly ambiguous. Early search engines looked for documents containing the words entered by the user into the search box . These are known as keyword search engines. Boolean search engines add a degree of sophistication by allowing the user to specify additional requirements. For example, "Tiger NEAR Woods AND (golf OR golfing) NOT Volkswagen" uses the operators "NEAR", "AND", "OR" and "NOT" to specify that these words must follow certain requirements. A phrase search is simpler to use, but requires that the exact phrase specified appear in the results. See also Concept Searching Limited Enterprise search Information retrieval References Information retrieval techniques