http://anthro.palomar.edu/animal/animal_1.htm
Here is a nice link showing how whne they started trying to classify all the animals on Earth, they assumed it had always been that way and always would be because er, god made everything. Then Darwin and Evolution showed how really complex it was. Genetics has helped simplify things again.
The lesson here is, when planning the information structure for your organisation, realise you are not god, there can be no simple hierarchical structure. Rather, realise that the relationship between information is primarily the people who create it, and also that it will always, always change.
