In the context of the World Wide Web, deep linking is a hyperlink either on a Web page or in the results of a search engine query to a page on a Web site other than the site’s home page. Typically, a Web site’s home page is the top page in the site’s hierarchy, and any page other than that is considered “deep.” (i.e. http://example.com/path/page), rather than the home page (i.e. http://example.com/).
Deep linking and HTTP
The technology behind the World Wide Web, the Hypertext Transfer Protocol (HTTP), does not actually make any distinction between “deep” links and any other links all links are functionally equal. This is intentional; one of the design purposes of the Web is to allow authors to link to any published document on another site. The possibility of so-called “deep” linking is therefore built into the Web technology of HTTP and URLs by default while a site can attempt to restrict deep links, to do so requires extra effort. According to the World Wide Web Consortium Technical Architecture Group, “any attempt to forbid the practice of deep linking is based on a misunderstanding of the technology, and threatens to undermine the functioning of the Web as a whole”.
Deep linking and web technologies
Websites which are built on web technologies such as Adobe Flash and AJAX often do not support deep linking. This can result in usability problems for people visiting such websites. For example, visitors to these websites may be unable to save bookmarks to individual pages or states of the site, web browser forward and back buttons may not work as expected, and use of the browser’s refresh button may return the user to the initial page.
However, this is not a fundamental limitation of these technologies. Well-known techniques, and libraries such as SWFAddress and unFocus History Keeper, now exist that website creators using Flash or AJAX can use to provide deep linking to pages within their sites.