From Wikipedia, the free encyclopedia.
A permalink (a portmanteau made by contracting the phrase "permanent link") is a type of URL designed to refer to a specific information item (often a news story or weblog item) and to remain unchanged permanently, or at least for a lengthy period of time to prevent link rot. The term was coined by Scott Banister and Matt Kerner in 1995, though the first implementation wasn't until March 2000 by Blogger co-founder Paul Bausch. Permanence in links is desirable when content items are likely to be linked to from, or cited by, a source outside the originating organization, and are desirable even within organisations when the complexity of websites grows to more than a modest number of pages. In particular, the growth of extensive commercial websites built on database-backed content management systems necessitated deliberate policies with regard to URL design and link permanence.
In the case of static HTML pages, for example for a blog, there are no links to entries per se but to the page with the latest entries. If the author posts many entries, this can mean that a specific entry is only accessible for several days, if that. In that case, web users who have previously stored a URL which referred to a specific story, discover after some time that it has become invalid.
The same happens in professional websites which have migrated from internal URL schemes based on the directories in which static html data was stored to all-dynamic storage, where all the pages served are generated on the fly by a database backend content management system.
Similarly, stories are sometimes given meaningless "magic cookie" names, and the (seemingly arbitrary) number used to generate these is often an internal database identifier integer. As articles are moved, deleted, and new articles created, the unique correspondence between articles and these database identifiers are lost, and again links can no longer be trusted to refer to the correct article after some time has passed.
With the increasing acceptance of web sources including online books and online journals in academic writing, permalinks are needed to ensure the quoted URL refers to the exact source and not a modified or updated version.
Permalinks typically consist of a string of characters which represent the date and time of posting, and some (system dependent) identifier (which includes a base URL, and often identifies the author, subscriber, or department which initially authored the item). Crucially, if an item is changed, renamed, or moved, its permalink remains unaltered. If an item is deleted altogether, its permalink cannot be reused.
Permalinks have subsequently been exploited for a number of innovations, including link tracing and link trackback in weblogs, and referring to specific weblog entries in RSS or Atom syndication streams.
Permalinks are supported in most modern weblogging and content syndicaton software systems, including Movable Type, LiveJournal, MediaWiki and Blogger.