Hierarchical Task Network (HTN) Planning José Luis Ambite*

35 Pages·2003·0.71 MB·English

by  Jose Luis Ambite

Hierarchical Task Network (HTN)
Planning
José Luis Ambite*
[* Based in part on presentations by Dana Nau and Rao Kambhampati]
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Hierarchical Decomposition
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Task Reduction
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Hierarchical Planning Brief History
(cid:131) Originally developed about 25 years ago
(cid:131) NOAH [Sacerdoti, IJCAI 1977]
(cid:131) NONLIN [Tate, IJCAI 1977]
(cid:131) Knowledge-based (cid:198) Scalable
(cid:131) Task Hierarchy is a form of domain-specific knowledge
(cid:131) Practical, applied to real world problems
(cid:131) Lack of theoretical understanding until early
1990’s
[Erol et al, 1994] [Yang 1990] [Kambhampati 1992]
(cid:131) Formal semantics, sound/complete algorithm,
complexity analysis
[Erol et al, 1994]
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Deployed, Practical Planners
(cid:131) SIPE, SIPE-2 [Wilkins, 85-]
(cid:131) http://www.ai.sri.com/~sipe/
(cid:131) NONLIN/O-Plan/I-X [Tate et. al., 77-]
(cid:131) http://www.aiai.ed.ac.uk/~oplan/
(cid:131) http://www.aiai.ed.ac.uk/project/ix/
(cid:131) Applications:
(cid:131) Logistics
(cid:131) Military operations planning: Air campaign planning, Non-
Combatant Evacuation Operations
(cid:131) Crisis Response: Oil Spill Response
(cid:131) Production line scheduling
(cid:131) Construction planning: Space platform building, house construction
(cid:131) Space applications: mission sequencing, satellite control
(cid:131) Software Development: Unix administrator's script writing
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Deployed, Practical Planners
Many features:
(cid:131) Hierarchical decomposition
(cid:131) Resources
(cid:131) Time
(cid:131) Complex conditions
(cid:131) Axioms
(cid:131) Procedural attachments
(cid:131) Scheduling
(cid:131) Planning and Execution
(cid:131) Knowledge acquisition tools
(cid:131) Mixed-initiative
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O-Plan
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HTN Planning
(cid:131) Capture hierarchical structure of the
planning domain
(cid:131) Planning domain contains non-primitive
actions and schemas for reducing them
(cid:131) Reduction schemas:
(cid:131) given by the designer
(cid:131) express preferred ways to accomplish a task
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HTN Formalization (1)
(cid:131) State: list of ground atoms
(cid:131) Tasks:
(cid:131) Primitive tasks: do[f(x , …, x )]
1 n
(cid:131) Non-primitive tasks:
(cid:131) Goal task: achieve(l) (l is a literal)
(cid:131) Compound task: perform[t(x , …, x )]
1 n
(cid:131) Operator:
(cid:131) [operator f(x , …, x ) (pre: l , …, l ) (post: l’ , …, l’ )]
1 n 1 n 1 n
(cid:131) Method: (α, d)
(cid:131) α is a non-primitive task and d is a task network
(cid:131) Plan: sequence of ground primitive tasks
(operators)
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