1. A method implemented by a computer comprising at least one processor for generating a document taxonomy based upon tag data in groupings of tags, the method comprising: retrieving into memory of a host computer different groupings of tags for correspondingly different documents providing a bottom-up view of the documents, the tags comprising meta-information provided by users to annotate bookmarks associated with the documents; deriving a folksonomy from the groupings of tags for the documents; establishing weights for the tags in the groups; inferring parent-child relationships amongst the groupings of tags based on sorting the tags for each document by the weights; organizing the folksonomy into a hierarchy of nodes based on the inferred parent-child relationships, each of the nodes being associated with a different subject in the folksonomy; and, publishing the hierarchy of nodes as a taxonomy for the documents to provide a top-down view of the documents.