A permalink, or permanent link, is a URL that points to a specific blog or forum entry after it has passed from the front page to the archives. Because a permalink remains unchanged indefinitely, it is less susceptible to link rot. Most modern weblogging and content-syndication software systems support such links. Other types of websites use permanent links, but the term permalink is most common within the blogosphere. Permalink is a portmanteau word made from permanent link. Permalinks are often simply stated so as to be human-readable.
One cited early use of permalink in its current sense was by Jason Kottke on March 5, 2000, in a post titled: "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 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. In response to Kottke's blog, on March 6, 2000, Matt Haughey posted the technical details on his own weblog, which helped open the way to widespread adoption.
Permanence in links is desirable when content items are likely to be linked to, from, or cited by a source outside the originating organization. Before the advent of large-scale dynamic websites built on database-backed content management systems, it was more common for URLs of specific pieces of content to be static and human readable, as URL structure and naming were dictated by the entity creating that content. Increased volume of content and difficulty of management led to the rise of database-driven systems, and the resulting unwieldy and often-changing URLs necessitated deliberate policies with regard to URL design and link permanence.
For example, Wikipedia's internal cgi-based URLs, e.g., http://en.wikipedia.org/w/index.php?title=Permalink, are re-written to a more human-readable form, http://en.wikipedia.org/wiki/Permalink.
An entry in a blog with many entries is accessible from the site's front page for only a short time. Visitors who store the URL for a particular entry often find upon their return that the desired content has been replaced by something new. Prominently posting permalinks is a method employed by bloggers to encourage visitors to store a more long-lived URL (the permalink) for reference.
Permalinks frequently consist of a string of characters which represent the date and time of posting, and an identifier which denotes the author who initially authored the item or its subject. Crucially, if an item is changed, renamed, or moved within the internal database, its permalink remains unaltered, as it functions as a magic cookie which references an internal database identifier. If an item is deleted altogether, its permalink can frequently not 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 and versions
Many blogging and content management systems do not support versioning of content, that is, if an entry is updated, a uniquely accessible version is not created. Thus, in the context of these systems, a permalink 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, the software which runs Wikipedia. In its current implementation, old revisions of specific articles, images, and templates are referenceable by unique unchanging URLs, although old versions of images and templates may not be utilized by current entries. Permanent links to specific versions are recommended for citing articles from sources such as Wikipedia and Wikinews, to ensure that the content remains unchanged for review. A reviewer can then view the cited revision, the current revision, and the differences between the two.
Popular permalink formats
Blogging software creators and blog hosting websites have not agreed on a standard format for permalink URLs. Some within the blogging community feel that standardization would lead to the practice of meta-information about articles being mined from the URLs themselves rather than an associated RSS stream or meta tags stored within the content. Although various permalink implementations accomplish essentially the same job, several vendors have produced different solutions.Movable Type and TypePad
http://.typepad.com//<4 digit year>/<2 digit month>/<15 character name>.htmlBlogspot
Comments, permalink, and what category the entry was posted to (known as metadata)
Permalinks are usually denoted by text link (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 employ their own symbol to represent a permalink such as an asterisk, a dash, a pilcrow (¶), or a unique icon.
Permalinks can be indicated within the HTML of a page so as to allow automated browsing tools to detect the permalink and use it for linking instead of the stated URL. The link element should include the following attributes: