Web Directories: A web directory or link directory is a directory of Web sites by subject on the World Wide Web which are most often created by humans. It specializes in linking to other web sites and classifying and categorizing those links often with a description. Many large directories include a keyword search option which usually eliminates the need to work through numerous levels of topics and subtopics.
The earliest Subject Directory search engine which covered WWW sites worldwide was The World Wide Web Virtual Library. It presented an alphabetical index of subjects and is based on Library of Congress Classification System. The most successful subject directory as well as subject directory search engine is probably Yahoo that was originated as a student run service, but now a profitable commercial site. It uses its own classification system.
a) Types: A web directory can be a real web directory that deals with all resources in all types of subject areas or it may only deal with the resources of a particular subject areas. In the latter case it is more commonly known as subject directory.
i) Subject Directories: A subject directory is a catalogue of sites collected and organized by humans in a specific subject only. Subject directories are often called subject "trees" because they start with a few main categories and then branch out into subcategories, topics, and subtopics.
ii) Subject Gateways: According to Place (2000), “Subject gateways are Internet- based services designed to help the users locate high quality information that is available on the Internet. They are, typically, data bases of detailed metadata (or catalogue) records which describes Internet resources and offer a hyperlink to the resources.” Users can choose to either search the database by keyword, or to browse the resources under subject headings”. Generally subject directory is treated as a broader term than that of Subject Gateways.
b) Importance: Because humans organize the websites in subject directories and it covers only a small fraction of the pages available on the web, one can often find a good starting point if the topic is included. Directories are also useful for finding information on a topic when you don't have a precise idea of what you need. They are also most effective for finding general information on popular or scholarly subjects.
Subject directory search engines are trying to compete with search engines. Web directories such as Yahoo and The Open Directory are, in a sense, the Internet equivalent of a public library and differ from the search engine in its provision of browsing the resources by some categories.
c) Examples: The following are some of the popular web directories-
i) Yahoo! (http://in.dir.yahoo.com/): Yahoo! aims to be the biggest Internet directories, with a high level of coverage and popular appeal as high priorities. It is an excellent site for finding topics that appeal to the general public. Currently, a search in Yahoo is being passed to AltaVista. However, people can still use its directory.
ii) Open Directory Project (http://dmoz.org/): Open Directory lists scholarly and popular websites. The Open Directory Project, also known as Directory Mozilla (DMOZ), relies on a volunteer work force of editors who, by selecting, classifying and cataloguing resources, are trying to build the largest library on the Internet. Mozilla was an early name for the Netscape Navigator Web browser. DMOZ is owned by Netscape Communications, but the information and database are freely available to other companies. The raw open-source directory is used by Google, Netscape Search, AOL Search, Lycos, HotBot, and DirectHit.
iii) BUBL Link (http://bubl.ac.uk/): BUBL Link uses the Dewey Decimal Classification system as the primary organization structure for its catalogue of Internet resources. It carefully selected and accurately catalogued many LIS resources. It was developed by Centre for Digital Library Research, Department of Computer and Information Sciences, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH, Scotland.
iv) About.com: At About.com (http://www.about.com/) you’ll find a directory with a twist. Each topic area has an assigned "Guide" responsible for writing articles and organizing links on the topic.
The other web directories include Internet Public Library (http://www.ipl.org/), Librarians' Index to the Internet (http://www.lii.org/), WWW Virtual Library (http://vlib.org/), Google directory (http://directory.google.com/), Looksmart, etc..
The Internet Library for Librarians (http://www.itcompany.com/inforetriever/) is a subject directory. UNESCO, IFLA, etc also have subject directories. Besides, many individual especially LIS professional also develop their subject directories, but because of space, we cannot do justice to all such sites.