(EN) The categories of media objects in a database are linked in a hierarchical tree system formed of nodes 201-211 with each node representing a category, there being a basic parent/sibling relationship between the nodes of the tree. Association links 212-215 link categories so that a user can traverse the tree by moving from a first category to a second category which need neither be at the same hierarchical level in the tree nor have any form of parent/sibling relationship.