Collaborative structured tagging enables a community of users to define different types of tags for online content. The diverse tag types provide a non-flat or dimensional tagging data structure that supports navigation and search for content, as well as comparison of the content. In one implementation, the collaborative structured tagging is employed in an item encyclopedia that offers community-authored information on various items in one or more electronic catalogs. In this context, the collaborative structured tagging facilitates comprehensive cross-product comparison and dimensional product navigation.