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Roger C. Schank and Robert P. Abelson (1977). Scripts, Plans, Goals and Understanding: an Inquiry into Human Knowledge Structures (Chap. 1-3), L. Erlbaum, Hillsdale, NJ

@Book{schank+abelson77,
  author =       "Roger C. Schank and Robert P. Abelson",
  title =        "Scripts, Plans, Goals and Understanding: an Inquiry
                 into Human Knowledge Structures",
  publisher =    "L. Erlbaum",
  year =         "1977",
  address =      "Hillsdale, NJ",
  keywords =     "PAM, SAM, TALE-SPIN, causality, conceptual dependency,
                 goals, plans, scripts, semantic primitive, text
                 understanding",
}

Author of the summary: David Furcy, 1999, dfurcy@cc.gatech.edu

Cite this paper for:

SYSTEMS: SAM (Script Applier Mechanism, described in chapter 8).
Understanding a situation means having been in that situation before (at least for conventional ones).
Understanding is knowledge-based and that knowledge is highly structured.
The concept of script.
A large part of understanding is script-based.
Two kinds of knowledge: specific (script-based) vs general.

Summary

Chapter 1 introduces the topic of the book, namely an enquiry into the nature of knowledge that is needed to understand the world and therefore to understand natural language. The main claim is that structured knowledge dominates understanding. The question is: "What is the content of these structures?" The authors take a pragmatic approach that does not separate form from content. Instead, they make a commitment to content (cf. the proposed conceptual primitives in the short introduction to CD in this chapter) but are not dogmatic about their specific choice. Note that their proposal has not been tested psychologically. This book is very much focused on memory, and in particular memory organization (in the first 3 chapters). In particular, the authors distinguish between semantic memory and episodic memory, and focus on the latter in which a script is a structured object representing a standardized generalized episode.

In chapter 2, the authors argue that understanding language involves causally connecting thoughts/sentences. Because causality is often implied or incompletely described, it is usually harder to understand connected text than individual sentences. Therefore, this chapter describes a formal representation (causal syntax) of causal chains which is to the discourse level what CD is to the sentence/thought level. Rules are provided in which every primitive action is associated with the set of states it can affect as well as those that enable it.

Chapter 3 describes scripts as groups of causal chains that represent knowledge about frequently experienced events (e.g. going to a restaurant). In other words, a script is a stereotyped sequence of actions that defines a well-known situation and has associated with it:

a number of roles for the actors (different points of view on the situation, e.g. customer vs waiter vs cook),
different tracks (e.g. restaurant, fast-food),
different scenes (e.g. enter, order, eat, pay); each scene has a MAINCON, i.e. a main conceptualization, which must have happened if the scene is instantiated,
as well as props, entry conditions, results, branches and loops etc.

Using scripts requires two mechanisms.

Script retrieval: A script is retrieved if a state is mentioned that constitutes a precondition for the script (e.g. the customer is hungry and has money) and there is a direct reference to a MAINCON or a prop in one of the scenes (e.g. order a dish or step to the counter).
Script application: An active script allows one to infer actions that were not stated (nor contradicted) as well as to instantiate roles etc. Hence the predictive power of scripts in conventional situations.

The restaurant script is called a situational script (standard social situation in a specific locale etc.). Other types of scripts include personal scripts (e.g. hitting on the waitress) and instrumental scripts (e.g. lighting a cigarette).

Many interactions can arise in script-based understanding, because several scripts are active at the same time (interference e.g. train and restaurant scripts), or because an action has an unexpected outcome which prevents the script from continuing normally or invokes another script recursively (within an existing script) - script in abeyance.

Of course, script-based understanding is only relevant when understanding stereotyped situations. Beyond these, it is necessary to have a model of the actors' goals and of the available plans to satisfy these goals. This kind of understanding is described in the rest of the book.

Summary author's notes:

none

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Last modified: Fri Oct 8 11:44:01 EDT 1999