Permalink

From Free net 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 blog item) and to remain unchanged permanently, or at least for a lengthy period of time to prevent link rot.

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History

The term was first used by Scott Banister and Matt Kerner in 1995, although this may not have referred to the same use of a unique, persistent URL for an individual item of content (in the same way that 'web log' was and still is used to refer to Apache traffic logs). The first use of a permalink in its current sense was by Jason Kottke on March 5, 2000, in a post titled: "Finally. Did you notice the", the first permalink being: http://www.kottke.org/00/03/finally-did-you-notice-the.

Matt Haughey had discussed a permalink style feature with Blogger co-founders, Evan Williams and Paul Bausch the previous weekend and Paul Bausch had pointed out that it was technically feasible to produce permanent links in Blogger, using a feature, written by him, that allowed the ID of a post to be placed in a Blogger template. The following day, March 6, 2000, Matt Haughey posted the details on his own weblog, which opened the way to widespread adoption.

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Purpose

Permanence in links is desirable when content items are likely to be linked to, from, or cited by, a source outside the originating organization. They 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 (e.g., blog pages) 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.

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 syndication software systems, including Movable Type, LiveJournal, and Blogger.

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Permalinks and versions

Many weblogging systems and content management systems do not support versioning of content, that is, if a record is updated, there is still only one single version of it. In the context of these systems, a permalink therefore may refer to different content over time. In the context of systems that support versioning, such as most wikis, a permalink is commonly understood as a link to a specific version. Here, both the link itself and the resource it refers to should not change over time.

One wiki implementation which supports this type of permalinks is MediaWiki. In the current implementation (as of January 2006), this does not include images and dynamically loaded templates: if they are changed, old versions use the new images and templates.

Permalinks to specific versions are recommended for citing articles from sources such as Wikipedia and Wikinews, to ensure that the content has not changed substantially by the time the reader looks at it. The reader can view the linked to revision, the current version, or the differences between the one the permalink refers to and any other version of the content.

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Popular permalink formats

Authors of blogging software and websites which host users weblogs have not agreed on 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 <meta> 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
http://<username>.typepad.com/<username>/<4 digit year>/<2 digit month>/<15 character name>.html
Blogspot
http://<username>.blogspot.com/<4 digit year>/<2 digit month>/<article name>.html
boastMachine
http://<site-specific prefix>/post/<blog_name>/<unique integer identifier>/<article name>
WordPress
http://<site-specific prefix>/<4 digit year>/<2 digit month>/<2 digit date>/<article name>/
LiveJournal and Bloglines
http://<username>.livejournal.com/<unique integer identifier>.html
http://users.livejournal.com/<username>/<unique integer identifier>.html for usernames beginning with an underscore
http://community.livejournal.com/<community name>/<unique integer identifier>.html for communities
Midgard CMS
http://<site-specific prefix>/midcom-permalink-<document unique identifier>
Typo
http://<site-specific prefix>/articles/<4 digit year>/<2 digit month>/<2 digit date>/<article name>
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Formatting

Blog entries are usually laid out as follows:

  • Title
  • Date
  • Entry
  • Comments, permalink, and what category the entry was posted to (known as metadata)

Permalinks are usually represented by text (i.e. "Permalink" or "Link to this Entry"), but sometimes a symbol may be used. The most common symbol used is the hash sign, or #. However, certain websites may have a "trademark" symbol, such as an asterisk or dash. Sometimes, this trademark character is used as a permalink instead. Recently, it has also become acceptable for the entry's title to serve as the permalink.

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Permalink detection

Permalinks can be displayed on the system using an HTML link element. This way authoring tools can automatically detect the permalink and use that for linking instead of the regular URL. The Link element should include the following attributes:

<link rel="bookmark" href="<Permalink URL>" />

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See also

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External links

fr:Permalien it:Permalink nl:Permalink pl:Odnośnik bezpośredni zh:PermaLink

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