Emergence of consensus and shared vocabularies in collaborative tagging systems

Valentin Robu*, Harry Halpin, Hana Shepherd

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

98 Citations (Scopus)


This article uses data from the social bookmarking site del.icio.us to empirically examine the dynamics of collaborative tagging systems and to study how coherent categorization schemes emerge from unsupervised tagging by individual users.

First, we study the formation of stable distributions in tagging systems, seen as an implicit form of "consensus" reached by the users of the system around the tags that best describe a resource. We show that final tag frequencies for most resources converge to power law distributions and we propose an empirical method to examine the dynamics of the convergence process, based on the Kullback-Leibler divergence measure. The convergence analysis is performed for both the most utilized tags at the top of tag distributions and the so-called long tail.

Second, we study the information structures that emerge from collaborative tagging, namely tag correlation (or folksonomy) graphs. We show how community-based network techniques can be used to extract simple tag vocabularies from the tag correlation graphs by partitioning them into subsets of related tags. Furthermore, we also show, for a specialized domain, that shared vocabularies produced by collaborative tagging are richer than the vocabularies which can be extracted from large-scale query logs provided by a major search engine.

Although the empirical analysis presented in this article is based on a set of tagging data obtained from del.icio.us, the methods developed are general, and the conclusions should be applicable across other websites that employ tagging.

Original languageEnglish
Article number14
Number of pages34
JournalACM Transactions on the Web
Issue number4
Publication statusPublished - Sept 2009


  • Algorithms
  • Measurement
  • Human Factors
  • Collaborative tagging
  • emergent semantics
  • complex systems
  • power laws
  • graphical models
  • knowledge extraction
  • community identification algorithms
  • search engines
  • del.icio.us


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