Advantages Revisit Web sites on a regular basis to look for changes or updates. Provide a ranking of search results based on relevancy. Disadvantages Rankings are sometimes questionable because they are computer-generated rather than human produced. Lack of human involvement can lead to poor quality control. They rely on individual submissions that are reviewed and indexed by subject category.
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.