But, the result of tagging can be a pretty flat list of many categories. There is a usefulness to a hierarchical ordering of information that enables people to browse and scroll down through categories. It can make it easier for people to find the information that they may be looking for.
A Ph.D. student from Stanford, Paul Heymann, has been working with Professor Hector Garcia-Molina to find a way to build Tag Hierarchies to make the efforts of tagging more useful. He notes that:
Tagging systems are excellent at the task that they were designed for—allowing a large, disparate group of users to collaboratively label massive, dynamic information systems like the web, media collections of millions of images, and so on. We are working to make these systems better by automating production of hierarchical taxonomies that describe the data from the raw flat tags generated by users.