User Interface for information navigation and data processing

A data processing apparatus includes a data storage portion, a category determination portion that determines to which of predetermined hierarchical tiers of categories each of pieces of data belongs, and a designation acceptance portion. The designation acceptance portion causes a selection acceptance screen for each of the tiers to be displayed, which includes a first object representing a group of pieces of the data in a tier currently of interest and second objects corresponding respectively to those ones of the categories which are in an immediately lower tier. Upon a predetermined narrowing-down action involving a selection of any one of the second objects being performed, the designation acceptance portion accepts a designation of one of the categories corresponding to the any one of the second objects. The second objects are disposed around the first object and each have a protruding portion protruding toward the first object.