P: 541. Complex data structures of fields within records, as well as
clustered, multilist, and inverted  files; key decoding by tree and
randomized techniques; overall techniques of classical document
retrieval  systems, e.g., the MEDLARS and NASA systems; overall
techniques of automatic document retrieval systems,  e.g., TIP and
SMART, the internal structure of SMART; question answering systems;
natural language  translation.