History and context
Labeling and tagging are carried out to perform functions such as aiding in classification, marking ownership, noting boundaries, and indicating identity. They may take the form of words, images, or other identifying marks. Analogous examples of tags in the physical world are graffiti and museum object tagging. In the organisation of information and objects, the use of textual keyword as part of identification and classification long use predates computers. However, computer based searching made the use of keywords a rapid way of exploring records. Online and internet databases and early websites deployed them 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.[1] 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.[2] The success of Flickr and the influence of Delicious popularized the concept,[3] 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.
Tags may be 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. Some researchers and applications have experimented with combining structured hierarchy and "flat" tagging to aid in information retrieval.[4]
Examples
Within a blog
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.
For an event
An official tag is a keyword adopted by events and conferences for participants to use in their web publications, such as blog entries, photos of the event, and presentation slides. Search engines can then index them to make relevant materials related to the event searchable in a uniform way. In this case, the tag is part of a controlled vocabulary.
Special types
Triple tags
A triple tag or machine tag uses a special syntax to define extra information about the tag, making it easier or more meaningful for interpretation by a computer program. Triple tags comprise three parts: a namespace, a predicate, and a value. For example, "geo:long=50.123456" is a tag for the geographical longitude coordinate whose value is 50.123456. This triple structure is similar to the Resource Description Framework model for information.
The triple tag format was first devised for geolicious[5] in November 2004, to map Delicious bookmarks, and gained wider acceptance after its adoption by Mappr and GeoBloggers[6] to map Flickr photos. In January 2007, Aaron Straup Cope at Flickr introduced the term machine tag as an alternative name for the triple tag, adding some questions and answers on purpose, syntax, and use.[7]
Specialized metadata for geographical identification is known as geotagging; machine tags are also used for other purposes, such as identifying photos taken at a specific event.
Hash tags
Short messages on services such as Twitter or identi.ca may be tagged by including one or more hashtags: words or phrases prefixed with a hash symbol (#),[8][9] such as those in:
#pilsner is my favourite kind of #beerAbout the Author: