Tagging

1. This is Michael's blog on Tagging. A tag is a non-hierarchical keyword or term assigned to a piece of information (such as an internet bookmark, digital image, or computer file). This kind of metadata helps describe an item and allows it to be found again by browsing or searching. Tags are chosen informally and personally by the item's creator or by its viewer, depending on the system. On a website in which many users tag many items, this collection of tags becomes a folksonomy.
   Tagging was popularized by websites associated with Web 2.0 and is an important feature of many Web 2.0 services. It is now also part of some desktop software. The use of keywords predates the internet and carried over to early websites as a way for publishers to help users find content. In 2003, the social bookmarking website Delicious provided a way for its users to add "tags" to their bookmarks (as a way to help find them later); Delicious also provided browseable aggregated views of the bookmarks of all users featuring a particular tag. Flickr allowed its users to add free-form tags to each of their pictures, constructing flexible and easy metadata that made the pictures highly searchable. The success of Flickr and the influence of Delicious popularized the concept, and other social software websites – such as YouTube, Technorati, and Last.fm – also implemented tagging. "Labels" in Gmail are similar to tags.
   Websites that include tags often display collections of tags as tag clouds. A user's tags are useful both to them and to the larger community of the website's users. This collective set of tags is known as a folksonomy.
   Tags are a "bottom-up" type of classification, compared to hierarchies, which are "top-down". In a traditional hierarchical system (taxonomy), the designer sets out a limited number of terms to use for classification, and there is one correct way to classify each item. In a tagging system, there are an unlimited number of ways to classify an item, and there is no "wrong" choice. Instead of belonging to one category, an item may have several different tags. Many blog systems allow authors to add free-form tags to a post, along with (or instead of) placing the post into categories. For example, a post may display that it has been tagged with baseball and tickets. Each of those tags is usually a web link leading to an index page listing all of the posts associated with that tag. The blog may have a sidebar listing all the tags in use on that blog, with each tag leading to an index page. To reclassify a post, an author edits its list of tags. All connections between posts are automatically tracked and updated by the blog software; there is no need to relocate the page within a complex hierarchy of categories.