Deep Web

Subject directories consist of websites arranged by topic for easy browsing. They are very useful in locating Deep Web Material.  This is because:

• Human beings, not machines, create subject directories, and select which sites a directory will include. 
• The creator of a directory may come across websites for possible inclusion in a variety of ways: via a search engine search, via a database search, from a colleague, through a printed publication, etc.  
• Some of these sites may therefore be part of the Deep Web. 
• Some of these sites may also be the initial page of a database website, which can lead to Deep Web material.

A federated search engine submits keyword searches to multiple search engines or databases simultaneously.  One attempt to extract Deep Web content has been to create federated engines which search multiple, subject-related databases.  Such federated search engines are called vertical search engines. 

When you use a vertical engine:

• Your keyword search automatically triggers keyword searches in a number of individual databases all at once.
• Together these databases may yield a great deal of topically related information which otherwise might have remained hidden, scattered across individual databases.

Vertical search engines include: