USER MODELS, DISCOURSE MODELS, AND SOME OTHERS
Karen Spärck Jones · OLAC - Open Language Archives Community
My context for this note is natural language interfaces to complex systems, considered, as the aim is system building, from the system's point of view. I hold that the discourse model relates four other models that are all required in dialog, but which need to be distinguished. These other models, as I define them in this note, are the world model, the user model, the system model, and the text model. It is a mistake, in my view, to try to establish the relation between discourse models and user models without reference to the other models that figure in the interaction between man and machine. The case for all the models mentioned can be made through a hypothetical system example. Suppose we have an automated reference librarian in an industrial company, i.e., a highly sophisticated expert system. Suppose also that the system can sustain the kind of dialog we can, and so imagine a dialog between the system and a user as follows: U1. I 'm looking for a book on logic programming. S1. You're in Accounts, aren't you? U2. Yes. $2. So you'd like something with financial examples. U3. Well that would be very convenient, but I 'm really interested in logic programming itself. $3. Just as well: we don't have anything on Prolog for accountants. Do you want something really noddy? We've got one pretty basic book. U4. How good do you think it is? $4. It's very popular. It doesn't assume you know anything about programming. U5. Oh, but I've done a bit of Cobol. $5. There isn't anything on Prolog from a Cobol point of view, I 'm afraid. U6. I wouldn't have thought that mattered: Cobol's a good general lead in, isn't it? $6. Not especially. But we have another book that would probably suit you better than the first: it's very clear and has a lot of different examples like planning the week's menus and building an office meeting diary system, but it does assume you have some experience of programming. I assume that the system knows about the material in the library, about the company, and about the library's role in the company's activities. It also knows about the company's employees (which include the illustrative user, known to be a woman in Accounts who thinks her boss underestimates her). The system's knowledge of the library and the company are part of its permanent world knowledge, and its knowledge of the company's employees is in principle no different in kind, though the system's knowledge of people's intensional states may be less certain than some of its other knowledge. There is nevertheless a good reason for distinguishing the system's knowledge of its users, and hence of any specific user, from the rest of its world knowledge. This is a functional reason: the system exists to solve problems presented by its users. The individual user is a necessary participant in the system's problem solving, and the system's actions are driven by its view of the user's specific needs. In the dialog, the system's response $6 is motivated by the perceived fact that the user, as a user, is a person with particular characteristics who is separated out from the rest of the world because her needs have to be met. Thus the response is an appropriate one in relation not to individual utterances or facts about the user, but to the entity constituting the user model as a whole, namely that she's a non-novice female, seeking to impress her boss by improving her computing skills. (This functional view, of course, implies that whether the user is human or not is an independent, contingent matter.) But for the same functional reason, the system has to have a model of itself embodying, for example, its plan to extract more detail about the user's book request. Though the system is in principle, like the user, part of the world, it has to be functionally distinguished for it to carry out its task: thus it is the system's aim, not the general state of the world, which leads it to choose $2, asking about financial examples.