Tag (metadata)

with terms related to Web 2.0]] In online computer systems terminology, 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 generally chosen informally and personally by the item's creator or by its viewer, depending on the system.

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.

History and context

Labeling and tagging are carried out to perform functions such as aiding in classification, marking ownership, noting boundaries, and indicating online identity. They may take the form of words, images, or other identifying marks. An analogous example of tags in the physical world is museum object tagging. In the organisation of information and objects, the use of textual keywords as part of identification and classification long 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. 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.

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.

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 semantic 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 in November 2004, to map Delicious bookmarks, and gained wider acceptance after its adoption by Mappr and GeoBloggers 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.

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 or naming species using binomial nomenclature.

=== Hash tags === Short messages on services such as Twitter or identi.ca may be tagged by including one or more hash tags: words or phrases prefixed with a hash symbol (#), with multiple words concatenated, such as those in:

: #realale is my favorite kind of #beer

Then, a person can search for the term #realale and this tagged word will appear in the search engine results. These hash tags also show up in a number of trending topics websites, including Twitter's own front page. One phenomenon specific to the Twitter ecosystem are micro-memes, which are emergent topics for which a hash tag is created, used widely for a few days, then disappears. For example, #ladiespleasestop, #oneletteroffmovies, #thingssaidb4sex, and #doyoumind were popular micro-memes in June 2009.

The feature has been added to other, non-short-message-oriented services, such as the user comment systems on YouTube and Gawker Media. Real-time search aggregators such as Google Real-Time Search also support hashtags in syndicated posts, meaning that hashtags inserted into Twitter posts can be hyperlinked to incoming posts falling under that same hashtag; this has further enabled a view of the "river" of Twitter posts which can result from search terms or hashtags.

Star tags

A star tag is a way for users to assign a numerical rating to their posts. The star tag is prefixed with the asterisk "*" and given a numerical value of 0 through 9 based on a user's rating. This is similar in concept to the rating systems used for Yelp or Amazon, but can be used in different services like Twitter or Facebook when discussing any subject or location. For example: : Just saw #inception - totally awesome movie! *9 or : Tried the new coffee shop on Main St and 5th... they need to change the water or something *1

Advantages and disadvantages

In a typical tagging system, there is no explicit information about the meaning or semantics of each tag, and a user can apply new tags to an item as easily as applying older tags. Hierarchical classification systems can be slow to change, and are rooted in the culture and era that created them. The flexibility of tagging allows users to classify their collections of items in the ways that they find useful, but the personalized variety of terms can present challenges when searching and browsing.

When users can freely choose tags (creating a folksonomy, as opposed to selecting terms from a controlled vocabulary), the resulting metadata can include homonyms (the same tags used with different meanings) and synonyms (multiple tags for the same concept), which may lead to inappropriate connections between items and inefficient searches for information about a subject. For example, the tag "orange" may refer to the fruit or the color, and items related to a version of Apple's operating system may be tagged "Mac OS X", "Leopard", "software", or a variety of other terms. Users can also choose tags that are different inflections of words (such as singular and plural), which can contribute to navigation difficulties if the system does not include stemming of tags when searching or browsing. Larger-scale folksonomies address some of the problems of tagging, in that users of tagging systems tend to notice the current use of "tag terms" within these systems, and thus use existing tags in order to easily form connections to related items. In this way, folksonomies collectively develop a partial set of tagging conventions.

Complex system dynamics

Despite the apparent lack of control, research has shown that a simple form of shared vocabularies emerges in social bookmarking systems. Collaborative tagging exhibits a form of complex systems dynamics, (or self organizing dynamics). Thus, even if no central controlled vocabulary constrains the actions of individual users, the distribution of tags that describe different resources (e.g., websites) converges over time to stable power law distributions. The number of tags allowed may also be limited to reduce spam.

Syntax

Some tagging systems provide a single text box to enter tags, so to be able to tokenize the string, a must be used. Two popular separators are the space character and the comma. To enable the use of separators in the tags, a system may allow for higher-level separators (such as quotation marks) or escape characters. Systems can avoid the use of separators by allowing only one tag to be added to each input widget at a time, although this makes adding multiple tags more time-consuming.

A syntax for use within HTML is to use the rel attribute value "tag" (i.e., rel="tag") to indicate that the linked-to page acts as a tag for the current context.

See also

Ontology

Semantic Web

References

External links

A Uniform Resource Name (URN) Namespace for Tag Metadata. Tim Bray. Internet draft, expires August 5, 2007.

Category:Computer jargon Category:Web 2.0 Category:Metadata Category:Reference Category:Information retrieval