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Apermalink orpermanent link is aURL that is intended to remain unchanged for many years into the future, yielding ahyperlink that is less susceptible tolink rot. Permalinks are often rendered simply, that is, asclean URLs, to be easier to type and remember. Most modern blogging andcontent-syndication software systems support such links. SometimesURL shortening is used to create them.
A permalink is a type ofpersistent identifier and the wordpermalink is sometimes used as a synonym ofpersistent identifier. More often, though,permalink is applied to persistent identifiers which are generated by acontent management system for pages served by that system. This usage is especially common in the blogosphere. Such links are not maintained by an outside authority, and their persistence is dependent on the durability of the content management system itself.
In the early years of the web, all content was static, and thus allhyperlinks pointed at a filename. Soon, though, many web pages becamedynamic, and many URLs began to include query terms.
One cited early use of the termpermalink in its current sense was byJason Kottke on March 5, 2000, in a post titled: "Finally. Did you notice the".[1]Matthew Haughey had discussed a permalink-style feature withBlogger co-foundersEvan 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'sblog, on March 6, 2000, Haughey posted the technical details on his own weblog,[2] which helped open the way to widespread adoption.[citation needed]
Permanence in links is desirable when content items are likely to be linked to, from, orcited by a source outside the originating organization. Before the advent of large-scale dynamicwebsites built ondatabase-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 internalCommon Gateway Interface-based URLs are made more readable by simplifying them. The internalURI for a Wikipedia article named Example, which ishttp://en.wikipedia.org/w/index.php?title=Example, is generated viaURL rewriting from the more human-readable external URL,http://en.wikipedia.org/wiki/Example.
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 that represent the date and time of posting, and an identifier that 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 amagic cookie that 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 linktrackback in weblogs, and referring to specific weblog entries inRSS orAtom syndication streams.
Bothpermalink andPURL (persistent uniform resource locator) are used as a persistent URL, and redirect to the location of the requestedweb resource. The main differences in the concepts are aboutdomain name andtime scale: PURL uses an independent dedicated domain name, and is intended to last fordecades; permalinks usually do not change the URL's domain, and are intended for use on timescales of years.
Many blogging and content management systems do not supportversioning 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 mostwikis, a permalink is commonly understood as a link to aspecific version. Here, both the link itself and the resource it refers to should not change over time.
MediaWiki, the software that runsWikipedia, supports this type of permanent link. In its current implementation, old versions of specific articles, images, and templates are referenceable by unique unchanging URLs, though current entries may not use old versions of images and templates. Permanent links to specific versions are recommended for citing articles from sources such as Wikipedia andWikinews, 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.
Blog entries are usually laid out as follows:
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 anasterisk, a dash, apilcrow (¶), asection sign (§), or a unique icon.
Permalinks can be indicated within theHTML of a page to allow automated browsing tools to detect the permalink and use it for linking instead of the statedURL. The link element should include the following attributes:
<linkrel="bookmark"href="http://example.com/bookmark/123/"/>
