Wikipedia can be considered to contain a fraction of humanity's knowledge. We have investigated the structure of Wikipedia and its evolution to gain insights into the general structure of knowledge. Wikipedia has a category system in place since 2004, where users can categorize articles, assigning them to categories. We have investigated the structure of the category system and its evolution over time.
We have compared this system to a classic system of organizing knowledge and also investigated how the category system divides actual articles into groups.