An Overview of Teton

<title>An Overview of Teton </title>
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<h1>An Overview of Teton</h1>

The motivation underlying Teton's design  is the incorporation of
goal reconstruction within a cognitive architecture. VanLehn and Bell
view goal reconstruction as both a practical tool and a close approximation
of capabilities possessed by humans. <p>

<h2> Goal Reconstruction </h2>

Goal reconstruction is the ability to resume problem solving after
an interruption without working through  all the steps that were completed
before the interruption. This ability to pick up where one left off entails
determining which  steps towards solving the problem need not be repeated.
One means for accomplishing this is to employ perceptions of the current
situation. If some external record is kept of the steps taken to solve 
a problem, the already completed steps may  be
determined by the evidence of their completion in the record. An example
of this approach is picking up mathematical computations where one left
off by looking  at the digits and scratch marks that were written down
before the interruption. In this example, determining where to resume
calculations constitutes
situated action -- action driven by perception. Performing the calculations
constitutes planned action -- action driven by planning.
VanLehn and Bell put forth goal reconstruction
as the means for achieving this oscillation bewteen situated and 
planned action. They argue this capability is present in all humans
and that it is task general. <p>  
   

<h2> Tetons's Approach to Goal Reconstruction </h2> 

Teton's architecture includes features that enable the blending of
situated and planned action. The architecture is based on a production 
system. Declarative knowledge is stored in the 
<i> working memory </i>. Procedural
knowledge in the form of operator specifications and contol rules
is stored in the <i> knowledge base </i>. Two  modifications
to this basic design facilitate goal reconstruction. <p>

An operator have four parts. It has a goal type which specifies the
goals for which the operator can be applied. It has preconditions
and a body which specify the woking memory elements reuired for application
and the effects of the operator on working memory respectively. The
fourth part is a shortcut condition. This specifies when the operator
can be assumed to have already been applied. Shortcut conditions
are central  to Teton's implementation of goal reconstruction.
They allow Teton  to skip over operators applied  before
an interruption.   <p>

Teton's  working memory has an enhancement to allow situated behavior.
The <i> situation </i> is a part of working memory that stores
Teton's representation of the environment. This representation serves
as the external record of the steps followed in problem solving.
The situation is used to determine which shortcut conditions are true and
thus to enable Teton to skip over operators when it resumes problem solving
after an interruption.
<p>.   
 

<h2>References</h2>

1. Kurt VanLehn and Willam Bell, "Goal Reconstruction: How
Teton Blends Situated and Planned Action", in VanLehn (Ed.) 
<cite>Architectures for Intelligence
</cite>, Lawrence Erlbaum Associates Inc., Hillsdale NJ,1990, pp. 41-60. <p>