Commercial portals are created to generate income and serve the general public. These services contain directories that link to a wide range of topics and often emphasize entertainment, commerce, hobbies, sports, travel and other interests not necessarily covered by academic directories. These sites seek to draw traffic in order to support advertising. As a part of this goal, the directory is offered in conjunction with a number of additional customer services. LookSmart is an example of a commercial portal.
Subject directories differ significantly in selectivity.
Consider the policies of any directory that you visit. The lines between directories, search engines and the deep Web are blurring. The deep Web is often represented by searchable news, phone books, dictionaries, maps, stock quotes, items in retail stores, multimedia files, etc. Directories are also present at some search engine sites, and sometimes their contents are searched along with content from the general Web. Directory results are sometimes placed before search engine results in order to steer users to the directory's content.