"(...) tagging system is not "controlled" in this sense (...), but I'm wondering whether its web-scale nature can provide some benefit that one would not expect."
"TagOntology is about identifying and formalizing a conceptualization of the activity of tagging, and building technology that commits to the ontology at the semantic level."
"They are built to be human-usable (...) are targeted primarily for storage/retrieval of personal information and serendipitous discovery of group information . (...) The development communities for each are abuzz with ideas for exploiting the structure"