Advantages Provide users with a subject directory and a short description of each site. Human involvement usually produces a higher relevancy of results. Disadvantages Contain far fewer records than active search engines. Meta search engines do not create their own databases. They rely on existing active and passive search engine indexes to retrieve search results.
Advantages Remove most duplication from search results.
Save users time by searching several search engines at once. Disadvantages Redundancies can occur in search results. Displayed results are often confusing. Specialized search engines offer additional features that active, passive and meta search engines do not provide. Google Indexes Web sites based on how many other popular sites have linked to them.