Common Tag is an open tagging format developed to make content more connected, accessible and engaging. Unlike text tags, Common Tags are references to unique, well-defined concepts, complete with metadata and their own URLs.  

Specifically, Common Tag format is based on RDFa, a standard mechanism for placing structured content within HTML documents. The format uses the URIs of concepts defined on the Web as a way of anchoring the meaning of Tag objects. Common concepts can be found, among others, in two big databases of structured content or controlled vocabularies, as librarians call it – Freebase and DBpedia.  

According to the Common Tag web site, "The Common Tag format was developed to address the current shortcomings of tagging and help everyone - including end users, publishers, and developers - get more out of Web content. With Common Tag, content is tagged with unique, well-defined concepts - everything about New York City is tagged with one concept for New York City and everything about jaguar the animal is tagged with one concept for jaguar the animal.” 

Faviki is involved in the development of the  new open tagging format – Common Tag, together with AdaptiveBlue, DERI (NUI Galway), Yahoo!, Zemanta, and Zigtag. This is the first time that this number of web companies have stepped together from day one to introduce a tagging standard.

Resources:

Common Tag - The New Semantic Layer by Website Magazine, June, 2009

Will You Implement Yahoo's Common Tag? by Search Engine Roundtable, June, 2009

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Denice MacDonald