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Before the introduction of permalinks (in around 1999) web users frequently discovered that URLs they had previously stored which referred to a specific story had, after some time, become invalid. This was a particularly common phenomenon when professional websites began to migrate from internal URL schemes based on the directories in which static html data was stored to all-dynamic storage, where all the pages served were generated on the fly by a database backed content management system.
Similar " link rot" phenomena followed when sites used the newer CMS technologies. URLs for stories were frequently given meaningless " magic cookie" names, and the (seemingly arbitrary) number used to generate these was often an internal database identifier integer. As articles were moved, deleted, and new articles created, the unique correspondence between articles and these database identifiers were lost, and again links could no longer be trusted to refer to the correct article after some time had passed.
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, and Blogger.
Authors of blogging software and websites which host users weblogs have not agreed a standard format for permalink URLs. Indeed, they may never do so, as some feel that meta-information about an article should be obtained from the associated RSS stream or from tags in the content itself, and that URLs shouldn't be "cracked" to obtain this information. Consequently, although various permalink implementations accomplish essentially the same job, several vendors have produced different solutions.
Movable Type and typepad.com:
Blogspot:
Wordpress:
LiveJournal / bloglines:
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