COLING 82, ,IT. Horeck2) (ed.) North.Holland Publishing Company © Academi~ 1982 Taking the Initiative in Natural Language Data Base Interactions: Justifying Why Bonnie Webber and Aravind Joshl Department of Computer and Information Science University of Pennsylvania Philadelphia PA 19104 I. Introduction In answering a factual database query, one often has the option of providing more than just the answer explicitly requested. As part of our research on Natural Language interactions with databases~ we have been looking at three ways in which the system could so "take the initiative" in constructing a response: (i) pointing out incorrect presuppositions reflected in the user's query [4,5]; (2) offering to "monitor" for the requested information or additional relevant information as the system learns of it [6,7]; and (3) providing grounds for the system's response i.e., "justifying why". The following responses illustrate "presupposition correctlon"~ "monitor offers" and "justification", respectively. This paper describes our research on producing justifications. ("U" refers to the user, "S" to the system.) U: Is John taking four courses? SI: No. John can't take any courses: he's not a student. $2: NoD three. Shall I let you know if he registers for a fourth? $3: No, three - CIS531, CIS679 and Linguistics 650. Database systems are growing more complex in both their domain models and reasoning capabilities. For many reasons, it is important that such systems be able to point the user to what responses follow from. In this regard, Justification differs from argument, whose role is to convince the listener. The role of justification is rather to give the listener an informed basis for either accepting the system's response or quest[onlng its premises or reasoning. There are at least three issues involved in producing Justifications: (I) what Justification does a query call for? (2) what justification can the system give? (3) What constitutes a clear and understandab]e justification? The first depends prlmarily on whether or not the user's perceived expectations have been fulfilled by the system's answer. For example, the use of "still" in a query indicates that the user expects that the potentially changing situation described in hls/her query has not in fact changed. U: Does anyone still have an Incomplete in CSE1107 $I: Yes, John does. $2: No. The last remaining Incomplete was made up on 1 December. If the user's expectation is correct (i.e., not all Ineompletes have been nkade up), then facts corroborating that expectation may constitute appropriate justification as in the "yes" answer above. If it isn't correct (as ~n the "no" case), then specifying the event that enabled the change may constitue a more appropriate justification. 413