Motivation
Many domains in which AI planning techniques can be profitably
employed are dynamic in nature. For example, military operations
planning and controlling a mobile robot both exhibit this
characteristic: during either plan generation or plan execution, the
state of the world can change dramatically as troops are dispatched to
an area or a robot navigates through a hallway. For such domains, it
is necessary that plan generation systems be sensitive to run-time
concerns and that plan execution systems be capable of invoking the
plan generator to address unexpected events at run-time.
Traditionally, generative planning and plan execution have been
considered distinct activities. This dichotomy has lead to the
development of generative planning systems that ignore execution issues and
reactive plan execution systems that cannot synthesize new plans at
run-time. Not surprisingly, different representations have developed
for defining operators for synthesizing and executing plans, making it
difficult to support tightly integrated plan generation and plan
execution systems.
Overview
SRI International has developed a framework called the Act formalism for
expressing the kind of procedural information required by both
plan-generation and plan-execution systems. At the heart of the formalism
is the Act structure, which corresponds to both an operator or
plan in the terminology of generative planners, and a plan
fragment or operating procedure in the terminology of plan
execution systems. Act structures (also referred to as Acts) provide a
common representation language that bridges the gap between these two types
of plan-based systems. Development of the Act formalism was motivated by
experience in combining a generative planning system, SIPE-2, and a reactive plan-execution system PRS-CL, to form the basis of the integrated planning
environment, Cypress. While the details of Acts
are tailored to these two specific planning systems, the underlying
philosophy of Acts applies more generally to many types of planning
formalisms.
The online postcript document The
Act Formalism provides a brief overview of the Act formalism,
including a BNF grammar specification of Act. Additional details on the
semantics and backgound on Act can be found in the references provided
below.
The Act Editor
The Act-Editor is a
graphical browsing and editing system for procedural knowledge expressed
as Acts. Through it, Acts can be created, viewed, and edited through
direct picotiral manipulation.
References
K. L. Myers and D. E. Wilkins,
"The Act Formalism", Version 2.2,
SRI International Artificial Intelligence Center, Menlo Park, CA, September 1997.
Abstract: Provides a brief overview of the Act formalism, including a BNF grammar specification of Act.
D. E. Wilkins and K. L. Myers,
"A common knowledge representation for plan generation and reactive execution,"
Journal of Logic and Computation, vol. 5, number 6, pp. 731--761, December 1995.
Abstract: The ability to integrate sophisticated planning
techniques with reactive execution systems is critical for nontrivial
applications. Merging these two technologies is difficult because the forms
of knowledge and reasoning that they employ differ substantially. The ACT
formalism is a language for representing the knowledge required to support
both the generation of complex plans and reactive execution of those plans in
dynamic environments. A design goal of ACT was its adequacy for practical
applications. ACT has been used as the interlingua in an implemented system
that links a previously implemented planner with a previously implemented
executor. This system has been used in several applications, including robot
control and military operations, thus attesting to its expressive and
computational adequacy.
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Karen L. Myers,
<myers@ai.sri.com>
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David E. Wilkins,
<wilkins@ai.sri.com>
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Artificial Intelligence Center
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