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Tags are labels for something. There exist different classification systems, e.g. taxonomies like the ones used by librarians or folksonomies.

In the context of Web 2.0, Tagging means sticking keywords to something (a resource link, a web page, a picture, ...). The agents who can create tags are professionals, authors and users. One object can be tagged with as many words as one desires because there are no restrictions.

See also: controlled vocabulary (its opposite), metadata and indexing

Other usages of tag: A label in syntax used in markup languages like XML to delimit an element.


Thomas Vander Wal invented the expression folksonomies in 2004. They are "naturally grown" collections of tags, i.e. implicit taxonomies that are built by people creating and using tags.

“In contrast to professionally developed taxonomies with controlled vocabularies, folksonomies are unsystematic and, from an information scientist's point of view, unsophisticated; however, for Internet users, they dramatically lower content categorization costs because there is no complicated, hierarchically organized nomenclature to learn. One simply creates and applies tags on the fly.” (Wikipedia:Folksonomy, 18:45, 14 September 2006 (MEST))

Since Folksonomies are open-ended by definition, they do have some advantages.

  • They can quickly respond to innovations, new interests, new ways of looking at things etc. and, concerning language, they reflect changing terminologies because they don’t have to respect a controlled vocabulary.
  • “Perhaps the greatest benefit of folksonomy is its relevance in the information retrieval sense of the term -- that is, the capacity of its tags to describe the "aboutness" of an Internet resource. After all, folksonomies are generated by people who have spent a great deal of time interacting with the content they tag.” (Wikipedia:Folksonomy, 18:45, 14 September 2006 (MEST))
  • A more intriguing argument is that they convey information at multiple layers, i.e. they are simultaneously systematic (will cover all sorts of interest of a given population), and personal and social (they also provide information about this population.

Of course there are also disadvantages to folksonomies.

  • They are polysemic (one word has several meanings, this is why we use sometimes disambiguation pages in this wiki).
  • For the same concept synonyms and various spellings may be used etc.
  • They can include all sorts of meta noise (e.g. wrong tags or badly spelled tags).
  • They can be too personal, created by one user and without any meaning for the rest of the Web community.

There are solutions to avoid some "noise", and supporters of tagging, such as Lars Pind (2005) and Marieke Guy and Emma Tonkin (2006), concentrate on this problem and propose some ideas to make folksonomies work better.

  • Suggesting existing tags canhelp people become more familiarized with the world of tags, avoiding inconsistencies, obvious tags or general “noise”.
  • Showing related tags and synonyms.
  • Using a layout device to show the most used tags (e.g. size, colour).
  • Once given a fixed domain, offering users a list of tags from which they have to choose.
  • Offering a checklist of questions that could be applied to the object being tagged to help people focus their attention on its most salient characteristic.

Apart from these practical devices that could be introduced to simplify the system, Marieke Guy and Emma Tonkin(2006) recognize the necessity of a tag etiquette. Though tagging is something retively new, a set of rules to organize this new world could be the simpliest solution to avoid lots of problems (see Semantic web). The community needs some fixed advice to follow in order to use this tool correctly and better exploit this possibility.

Collaborative tagging

“Collaborative tagging describes the process by which many users add metadata in the form of keywords to shared content.” (Golder & Huberman, 2006).

(Collaborative) Tagging is used in many social software applications. Most of these are folksonomies, for example, to:

  • manage one's own digital artifacts and links;
  • allow people to share links (social bookmarking) and artifacts;
  • link people with similar interests (“Tagging will help social groups form around shared semantics, in addition to shared semantics arising from, and helping to define, groups” Weinberger, 2005, retrieved April 20, 2007);
  • calulate recommendations for a product (e.g. like Amazon does with keywords describing books).

Rashmi Sinha (2006) in her social analysis on tagging recognizes that “The basic social formations supported by tagging are more like crowds than true groups.” The system connects people who share one word, but they do not really know each other, nor do they know what the ideas the others link with the concept they use for tagging something are. However, collaborative tagging transforms people's individual experience on the Web into a social one which makes the wide world of Internet a little bit smaller and more friendly.

Why does it work ?

Firstly, it's easy for users and requires only two steps of cognitive processing (Sinha, 2005). In contrast, filling in metadata forms is time-consuming, boring and difficult.

Secondly, metadata are ridid and don't work in the real world. An object is not always either type 1 or type 2, but can be both or in between.

Metrics and visualization techniques can put some "order" into a big "tag soup", e.g. show which tags are close (e.g. see tag clouds) and therefore create "natural taxonomies".

“Tagging repudiates one of the deepest projects our culture has undertaken over and over again: The rendering of all knowledge into a single, universal framework. The semi-chaotic state of the “tagosphere” represents the nature of our shared world better than the cool marble columns of the old mono-order ever could” (Weinberger, 2005, retrieved April 20, 2007).


Metadata taxonomies vs. folksonomies

  • Some people hate metadata (DSchneider does because it's too much work)
  • Some people hate tagging (DSchneider does because within large crowds some people may unintentionnally or intentionnally use wrong tags, and because it also means extra work. :)

Also see the way MediaWikis use categories, which is a sort of bookmarking. Each author can assign a category to a page. If it doesn't exist, the wiki engine creates a "wanted Category" page that needs to be edited in order to display the automatically generated list of pages. Categories can also be inserted into Categories (which turns it into a subcategory of the give category). Note: Categories in this wiki were made by a single user DSchneider. It's something in between a little folksonomy and reflection about our field.


  • Rashmi Sinha's blog entries on tagging


Tag extractors



  • Farrell, Stephen and Tessa Lau, Fringe Contacts: People-Tagging for the Enterprise, WWW '2006 paper, PDF
  • Golder, Scott and Bernardo A. Huberman (2006). "Usage Patterns of Collaborative Tagging Systems." Journal of Information Science, 32(2). 198-208. Abstract/PDF
  • Guy, Marieke, & Tonkin, Emma (January 2006). “Folksonomies: Tidying up tags?”, D-Lib Magazine, 12, HTML
  • Pind, Lars (January 23, 2005). Folksonomies: how we can improve the tags, HTML
  • Sinha, Rashmi (2005). A cognitive analysis of tagging, (or how the lower cognitive cost of tagging makes it popular), HTML
  • Sinha, Rashmi (2006). A social analysis of tagging (or how tagging transforms the solitary browsing experience into a social one), HTML
  • Speller, Edith (February 2007). “Collaborative tagging, folksonomies, distributed classification or ethnoclassification: a literature review”, Library Student Journal, London, HTML
  • Vuorikari, Riina (2005), Social networking software and e-portfolios foster digitallearning networks, Special Insight Reports, European Schoolnet. HTML
  • Vuorikari, Riina (2005), Innovation Brief: Can personal digital knowledge artefact's managment and social networks enhance learning ? PDF
  • Vuorikari, Riina (2007). Folksonomies, social bookmarking and tagging: the tate-of-the-art, Special Insight Reports, Abstract/PDF. Recommended reading by Daniel K. Schneider.
  • Weinberger, David (May 13, 2005).Tagging and Why It Matters, Fellow, Harvard Berkman Center for the Internet and Society, PDF