Case Systems for Natural Language

In nany la;.RuaRes (e.g. Latin, Greek, Russian, Turkish, German) the relationship cf a noun phrase to the rest of a sentence is indicated by altered forms of the noun. The possible relationships are ealleo (surface) "cases". Because (1) it is difficult to specify semantic-free selection rules for the cases, and (?) related phenomena based on prepositions or word order appear in apparently case-less languages, many have argued that studies of cases should focus on meaninr, i.e. on "deep cases". Deep cases bear a close relationship to the modifiers of a concept. In fact, one could consider a deep case to be a special, or distinguishing, modifier. Several criteria for recon-izing deep cases are considered here in the context of the problem of describing an event. Unfortunately, none of the criteria serves as a completely adenuate decision procedure. A notion based on the context-dependent "importance" of a relation appears as useful as any rule for selecting deep cases. A represent?.tive sample of proposed case systems is exanined. Issues such as surface yers.us deep versus conceptual levels of cases, and the efficiency of the representations implicit in a case system are also discussed . Heport No. 3010 Bolt Beranek and Newman Inc TABLE OF CONTENTS PAGE