Scripts, Plans and Knowledge

"Of what a strange nature is knowledge! It clings to the mind, when it has once seized on it, like a lichen on the rock," Abstract We describe a theoretical system intended to facilitate the use of knowledge In an understand­ ing system. The notion of script is introduced to account for knowledge about mundane situations. A program, SAM, is capable of using scripts to under­ stand. The notion of plans is introduced to ac­ count for general knowledge about novel situa­ tions. I. Preface In an attempt to provide theory where there have been mostly unrelated systems, Minsky (1974) recently described the as fitting into the notion of "frames." Minsky at­ tempted to relate this work, in what is essentially language processing, to areas of vision research that conform to the same notion. Mlnsky's frames paper has created quite a stir in AI and some immediate spinoff research along the lines of developing frames manipulators (e.g. Bobrow, 1975; Winograd, 1975). We find that we agree with much of what Minsky said about frames and with his characterization of our own work. The frames idea is so general, however, that It does not lend itself to applications without further specialization. This paper is an attempt to devel­ op further the lines of thought set out in Schank (1975a) and Abelson (1973; 1975a). The ideas pre­ sented here can be viewed as a specialization of the frame idea. We shall refer to our central constructs as "scripts." II. The Problem Researchers in natural language understanding have felt for some time that the eventual limit on the solution of our problem will be our ability to characterize world knowledge. Various researchers have approached world knowledge in various ways. Winograd (1972) dealt with the problem by severely restricting the world. This approach had the po­ sitive effect of producing a working system and the negative effect of producing one that was only minimally extendable. Charniak (1972) approached the problem from the other end entirely and has made some interesting first steps, but because his work is not grounded in any representational sys­ tem or any working computational system the res­ triction of world knowledge need not critically concern him. Our feeling is that an effective characteri­ zation of knowledge can result in a real under­ standing system in the not too distant future. We expect that programs based on the theory we out­ …