Understanding Pragmatically Ill-Formed Input

UNDERSTANDING PRAGMATICALLY ILL-FORMED INPUT FL Sandra Carberry Department of Computer Science University of Delaware Newark, Delaware 19711 USA ABSTRACT An utterance may be syntactically and semant- Ically well-formed yet violate the pragmatic rules of the world model. This paper presents a context-based strateEy for constructing a coopera- tive but limited response to pragmatlcally ill- formed queries. Sug~estlon heuristics use a con- text model of the speaker's task inferred from the preceding dialogue to propose revisions to the speaker's ill-formed query. Selection heuristics then evaluate these suggestions based upon seman- tic and relevance criteria. I INTRODUCTION An utterance may be syntactically and semant- ically well-formed yet violate the prasmatlc rules of the world model. The system will therefore view it as "ill-formed" even if a native speaker finds it perfectly normal. This phenomenon has been termed "pragmatic overshoot" [Sondheimer and Weischedel,1980] and may be divided into three classes: [ I] User-specifled relationships that do exist in the world model. [2] not EXAMPLE: "Which apartments are for sale?" In a real estate model, single apart- ments are rented, not sold. However apart- ment buildings, condominiums, townhouses, and houses are for sale. User-specified restrictions on the relation- ships which can never be satisfied, even with new entries. EXAMPLE: "Which lower-level English courses have a maxim,-, enrollment of at most 25 students?" In a University world model, it may be the case that the maxim,-, enrollments of This material is based upon work supported by the National Science Foundation under grants IST- 8009673 and IST-8311400 lower-level English courses are constrained to have values larger than 25 but that such constraints do not apply to the current enrollments of courses, the maximum enroll- ments of upper-level English courses, and the maximum enrollments of lower-level courses in other departments. The sample utterance is pragmatically ill-formed since world model constraints prohibit the restricted relations specified by tbe user. [3] User-specifled relationships which result in a query that is irrelevant to the user's underlying task. EXAMPLE: "What is Dr. Smlth ' s home address?" The home addresses of faculty at a university may be available. However if a student wants to obtain special permission to take a course, a query requesting the instructor's home address is inappropriate; the speaker should request the instructor's office address or phone. Although such utterances do not violate the underlying domain world model, they are a variation of pragmatic overshoot in that they violate the listener's model of the speaker's underlying task. A cooperative partlc/pant uses the informa- tion exchanged during a dialogue and his knowledge of the domain to hypothesize the speaker's goals and plans for achieving those goals. This context model of goals and plans provides clues for inter- preting utterances and formulating cooperative responses. When pragmatic overshoot occurs, a human listener can modify the speaker's ill-formed query to form a similar query X that is both mean- ingful and relevant. For example, the query "What is the area of the special weapons mag~azine of the Alamo?" erroneously presumes that storage …

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