Entity-Oriented Parsing

Entity-Oriented Parsing Philip J. Hayes Computer Science Department, Carnegie.Mellon Llniversity Pi~tsbur~ih, PA 152_13, USA Abstract f An entity-oriented approach to restricted-domain parsing is proposed, In this approach, the definitions of the structure and surface representation of domain entities are grouped together. Like semantic grammar, this allows easy exploitation of limited dolnain semantics. In addition, it facilitates fragmentary recognition and the use of multiple parsing strategies, and so is particularly useful for robust recognition of extragrammatical input. Several advantages from the point of view of language definition are also noted. Representative samples from an enlity-oriented language definition are presented, along with a control structure for an entity-oriented parser, some parsing strategies that use the control structure, and worked examples of parses. A parser incorporaling the control structure and the parsing strategies is currently under implementation. 1. Introduction The task of lypical natural language interface systems is much simpler than the general problem of natural language understanding: The simplificati~ns arise because: 1. the systems operate within a highly restricted domain of discourse, so that a preci..~e set of object types c;~n be established, and many of tl;e ambiguities that come up in more general natural language processing can be ignored or constrained away; 2. even within the restricted dolnain of discourse, a natural language i.terface system only needs to recognize a limited subset of all the Ihings that could be said -- the subset that its back-end can respond to. The most commonly used tr:chnique to exploit these limited domain constraints is semantic ~j~amrnar [I, 2, 9] in which semantically defined categories (such as <ship> or <ship- attrihute>) are used in a gramrnur (usually ATN based) in place of syntactic categories (such as <noun> or <adjective>). While semantic grammar has been very successful in exploiting limited domain constraint.~ to reduce ambiguities and eliminate spurious parses of grammatical input, it still suffers from the fragility in the face of extragrammatical input characteristic of parsing based on transition nets [41. AI~o. the task of restricted-domain language definition is typically difficult in interlaces based on semantic grammar, in part bscaus~ th.,: grammar definition formalism is not well imegrated with the method of d~..fining the object and actions of tl~e domain of discourse (though see [6]). 1This r~t,;e~rch wmJ spont;(.cd by the At; Fnrco Office of Scient=fic Resr.,'l¢,";h und{;r Cow,tract AFOC, R-82-0219 ]his paper proposes an alternat;ve approach to restricted domain langua~fe recognition calI~d entity-oriented p;rsing. Entity-orie=-ted parsing uses the same notion of semar~tlcally- defined catctjeries a.', ~2mantic grammar, but does net embed these cate,:.iories in a grammatical structure designed for sy.tactic recognition. Instead, a scheme more reminiscent of conceptual or case.frame parsers [3, 10, II] is employmf. An entity-oriented parser operates from a collection of definitions of the various entities (objects. events, cem, m~mds, states, etc.) that a particular interf:~ce sy-~teln needs to r:.~cognize. These definitions contain informatiol~ about the internal structure of the entities, about the way the entitie:~ will be manifested in the natural language input, s~}(I about the correspondence belween the internal …

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