Abstract: A system for retrieving information units from a data structure. The system includes a search engine and an on-screen user interface. The data structure includes a dictionary file having keywords related to each other by a hierarchy, wherein each information unit is associated with a keyword. The user interface provides a text input zone to define a search and a user control to order the search engine to perform the search depending on the contents of the text input zone. The user interface also provides a first on-screen list display zone for showing results of the search performed by the search engine and a second list display zone for showing the results from the hierarchy related to the results shown in the first display zone.