A web directory is not a search engine, and does not display lists of web pages based on keywords, instead it lists web sites by category and subcategory. The categorization is usually based on the whole web site, rather than one page or a set of keywords, and sites are often limited to inclusion in only one or two categories. Web directories often allow site owners to directly submit their site for inclusion, and have editors review submissions for fitness.
RSS directories are similar to web directories, but contain collections of RSS feeds, instead of links to web sites.
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[edit] General
Some directories are very general in scope and list websites across a wide range of categories, regions and languages. But there are also a large number of niche directories, which focus on restricted regions, single languages, or specialist sectors.
Examples of well known, general, web directories are Yahoo! Directory and the Open Directory Project (ODP). ODP is significant due to its extensive categorization and large number of listings and its free availability for use by other directories and search engines (many sites violate its terms of use by using its content without acknowledgement).
A debate over the quality of directories and databases continues, as search engines use ODP's content without real integration, and some experiment using clustering. There have been many attempts to make directory development easier, whether using a "links for all" type link submission site using a script, or any number of available PHP portals and programs. Recently, social software techniques have spawned new efforts of categorization, with Amazon.com adding tagging to their product pages.
Directories have various types of listings, often dependent upon the price paid for inclusion:
- Free Submission - there is no charge for review of the site
- Reciprocal Link - the site submitted must link back to the directory in order to be listed
- Paid Submissions - a fee is charged for reviewing the submitted link
- No Follow - there is a rel="nofollow" attribute associated with the link, meaning search engines will not follow the link.
- Featured Link - the link is given a premium position in the category where it is submitted
- Featured Homepage Link - the link may be listed on the homepage of the directory.
- Bid for Position - a recent innovation (2007) where sites are ordered based on bids
[edit] Human-edited directories
A human-edited directory is created and maintained by editors who add links based on the policies particular to that directory.
Human-edited directories are often targeted by SEOs on the basis that links from reputable sources will improve rankings in the major search engines. Some directories may prevent search engines from rating a displayed link by using redirects, nofollow attributes, or other techniques.
Many human-edited directories, including the Open Directory Project and the World Wide Web Virtual Library, are edited by volunteers, who are often experts in particular categories. These directories are sometimes criticized due to long delays in approving submissions, or for rigid organizational structures and disputes among volunteer editors.
In response to these criticisms, some volunteer-edited directories have adopted wiki technology, to allow broader community participation in editing the directory (at the risk of introducing lower-quality, less objective entries).
Another direction taken by some web directories is the paid for inclusion model. This method enables the directory to offer timely inclusion for submissions and generally fewer listings as a result of the paid model. They often offer additional listing options to further enhance listings, including features listings and additional links to inner pages of the listed web site. These options typically have an additional fee associated, but offer significant help and visibility to sites and/or their inside pages.
Today submission of websites to web directories is considered as a common SEO (search engine optimization) technique to get vital back-links for the submitted web site. One distinctive feature of 'directory submission' is that it can not be fully automated like search engine submissions. Manual directory submission is a tedious and time consuming job and is often outsourced by the webmasters