Almost all directories allow users to submit pages to its database. If there are no reviewers of the pages before being posted, pages are placed where the person submitting the page feels it is best appropriate. This may limit the searcher's ability to retrieve an appropriate page. If no review to submissions is conducted, then the quality of the page is unknown to the searcher. Search Engines Advantages Search engines maintain databases of websites gathered by using a program called a spider.
Spiders crawl the web and bring back sites to enter into the database.
Search engines also allow users to submit sites. The sizes of the databases vary greatly and can affect the results. Using keywords, search requests produce lists of sites for the user reducing the number of clicks necessary to get to actual websites. Disadvantages The quality and size of the databases vary widely. Search strategies affect the results.