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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
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
Author of the summary: David Furcy, 1999, firstname.lastname@example.org
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.
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:
Using scripts requires two mechanisms.
- 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.
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).
- 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.
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:
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Last modified: Fri Oct 8 11:44:01 EDT 1999