The structuring of data items in a hierarchical structure. A user interface permits a user to define, for each generation of a hierarchical tree, the child characteristics for child data items of particular nodes in the hierarchical tree. Then, a query, or a query template, may be formulated using the child characteristic and the designated parent data item. This may be repeatedly performed to allow for multiple generations of data items to be formed. The query may, at some point, be submitted to identify which data items are child data items or the parent data item. The data items that result from the query (or at least a portion of the data items) may then be assigned as child data items of the parent data item. The query may be postponed until the node is expanded by the user.