Subject Directories contain selected sites arranged by subject categories. This is similar to the subject headings used in the inline catalog. When you are exploring the subject categories, you are using Controlled Vocabulary . Yahoo is one of the most popular general directories. Biosis, another subject directory is limited to biology.
Subject directories are best for broad searches.
Indexes will find pages full of links on a subject. Boolean search strategies AltaVista Advanced Search lets you use Boolean logic. Searching Results Relevancy rankings Search engines give some measure of quality of the match by giving a relevance score. These scores reflect the number of times a search term appears and where it appears. More weight is given if the term appears in the title or in the beginning of the document or if the words are close to one another.