Page 80 - Introduction to AI Robotics

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2.8 Exercises
chitecture will suffer from the frame problem. The Hierarchical Paradigm
was introduced in the first mobile robot, Shakey. Strips is an important plan-
ning technique that came out of the Shakey project at SRI, which focused
on the PLAN primitive in robotics. Concepts and terms which emerged that
continue to play an important role in defining robotics are: preconditions,
the closed and open world assumptions, and the frame problem. Hierar-
chical systems have largely fallen out of favor except for the NIST Realtime
Control Architecture. The decline in popularity is due in part to its focus on
strong niche targetability at the expense of true modularity and portability.
However, as will be seen in the following chapters, insights from biology and
cognitive science have led to paradigms with more intuitive appeal. One of-
ten overlooked property of most hierarchical architectures is that they tend to
support the evolution of intelligence from semi-autonomous control to fully
autonomous control.

2.8 Exercises

Exercise 2.1
Describe the Hierarchical Paradigm in terms of a) the SENSE, PLAN, ACT primitives
and b) sensing organization.
Exercise 2.2
Define the following terms in one or two sentences. Give an example of how each
arises in a robotic system:

a. precondition
b. closed world assumption
c. open world
d. frame problem

Exercise 2.3
Consider the frame problem. Suppose the World Model for a Strips-based robot con-
sisted of 100 facts. Each fact requires 1KB of memory storage. Every time a new object
is added to the world model, it increases the model by 100 (a linear increase). One
object, 100 facts, 100KB of storage; two objects, 200 facts, 200KB. How many objects
would fill 64KB of memory?

Exercise 2.4
Redo the above exercise where the number of facts in the world model doubles every
time a new object is added (exponential). One object, 100 facts, 1KB, two objects,
200 facts, 200KB, three objects, 400 facts, 400KB. Which is a more reasonable rate to
assume the world model would increase at, linear or exponential?