NOT The Boolean operator NOT excludes the word that follows it. This operator is helpful in eliminating a subset of documents from the search. Canine NOT dog will exclude all documents in which the term dog is found. Use of this operator will usually retrieve a large number of documents. The indexed material is not reviewed for quality.
Search engines give the researcher the largest possible selection of raw material.
Edited search engines filter materials before you see them. They may judge sites by the quality of the material presented, and the amount of material on the site. These search engines often exclude sites that contain objectional material. Hierarchical Indexes List subjects similarly to the traditional card catalog. The researcher can browse subject listings instead of searching for specific keywords.