Action Relations in Rationale Clauses and Means Clauses

ACTION RELATIONS IN RATIONALE CLAUSES AND MEANS CLAUSES* CECILE T. BALKANSKI Aiken Computation Lab, Harvard University Cambridge, MA 02138, U.S.A Abstract Communication among agents collaborating on a task often involves complex utterances about multiple ac- tions. In this paper, we analyze two particular multi- action constructions, utterances with means clauses and utterances with rationale clauses. We present the distinctive features of these constructions, de- scribe their logical form, and define interpretation rules for deriving their meaning in terms of the gener- ation, enablement and Contributes relations between actions which have been motivated independently by research in plan recognition. We also demonstrate that these rules yield the appropriate properties of ratio- nale clauses and means clauses and show how these constructions can be distinguished algorithmically. 1 Introduction Communication among agents collaborating on a task often involves complex utterances about multiple ac- tions, as illustrated in the following example: By going and getting the key and then coin- ing and unlocking the grate, for that you get a ccrtain number of points, and then as you collect treasures, you get more points. [1] Multi-action utterances like these present two par- ticular challenges for natural language interpretation systems: determining an appropriate representation of their meaning, and defining the process by which this representation can be derived from natural language utterances. Substantial work has been done on the de- velopment of logical forms as a necessary step toward the goal of representing the meaning of an utterance. However, very little is yet established on the represen- tation of the information communicated in complex action utterances like the one given above, and still less on the interpretation of thc relations tbat connect the actions described in these utterances. In this paper, we analyze two particular multi-action constructions, utterances with rationale clauses and utterances with means clauses, illustrated respectively in (la) and (tb) below, with the goal of meeting, at *I would like to thank Barbara Grosz, Andrew I(ehler, l(aren Lochbaum, Stuart Shieber and Candy Sidner for helpful com- ments regarding tiffs paper. This researdt has I)een supported by U S WEST Advanced Technologies, by the Air Force Office of Scientific Research under Contract No.AFOSR-89-0273, and by an IBM Graduate Fellowshila. ACRES DE COLING-92, NANTES, 23-28 h0~r 1992 2 6 7 least in part, these two challenges. As their names suggest, means clauses express the means by which an action is performed, while rationale clauses express the reason, or rationale, of the main clause action. In the last section of this paper, we show how to distin- guish rationale clauses from two superficially similar constructions: purpose clauses, as in "Mary bought a suit to wear at the meeting", and infinitival relative clauses, as in "John found the book to give to his sis- ter". (1) ~. Mary pressed the button to reset the printer. b. Mary reset tbe printer by pressing the button. Rationale clauses and means clauses are of interest not only as exemplars of multi-action utterances, but also because of the subtle differences in …

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