Temporal Plans and Resource Management

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Temporal Plans and Resource Management

• Pieter Buzing Cees Witteveen
• Delft University of Technology

2
What about?

• Temporal planning in multi-agent systems
• or distributed issues in planning systems
• Plan repair (during tactical phase)
• Introduce resource-based view
• Use scheduling heuristic
• Integrate it with multi agent temporal planning

3
The Problem

• Many complex environments need planning and
  coordination of actions
• Example airport, harbor, factory,
• Multiple (autonomous) parties involved
• Issues conflicting goals, communication,
  coordination
• Execution phase is error-prone
• Environment is unpredictable, partial information

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Example Airport
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Solution Requirements

• Respect individual planning tools
• Abstract temporal plan model
• Handle aberrations during plan execution
• Flexibility encoded in plan
• Respect and use agents intelligence
• No central planner
• Smart coordination (negotiation)

6
10, 20
8, 30
15, 25
5, 20
14, 20
12, 25
10, 40
11, 15
10, 21
10, 15
7, 21
10, 12
5, 30
1, 10
4, 6
5, 25
5, 10
8, 23
13, 26
12, 20
10, 15
5, 24
12, 35
10, 20
7, 15
5, 15
5, 20
12, 21
15, 16
8, 30
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Simple Temporal Problem (STP)

• Planning as CSP (Dechter et.al., 1991)
• Temporal constraints between time point variables
• Path consistency arc consistency polynomial
  time O(n3)
• Extracting schedule is simple (read all lower
  bounds)
• Flexibility is maintained

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STPs and Preferences

• Duration action A is 10, 40 hard constraint
• In practice
• A takes about 25 minutes, perhaps bit more/less
• 25 would be ideal, but 15-30 is okay
• Soft constraint expressed as preference function
• Repair opportunities

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Preferences and Repair

• During planning
• Iteratively solve STPs at increasing p-levels
• Best plan is selected
• During execution
• Some disruption causes a constraint change
• Return to less-preferred (but feasible) STP
• Example
• Scheduled duration action A at p3 is 23, 25
• Oops! Action A will take 28 minutes conflict!
• But we have a backup solution at p1

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STPs and Resources

• Planning action ordering
• Scheduling resource assignment
• Practical planning problems are mix of both
• Airport gates, runways, taxiways
• Example 4 flights scheduled on 2 gates

11
10, 20
8, 30
15, 25
5, 20
14, 20
12, 25
10, 40
11, 15
10, 21
10, 15
7, 21
10, 12
5, 30
1, 10
4, 6
5, 25
5, 10
8, 23
13, 26
12, 20
10, 15
5, 24
12, 35
10, 20
7, 15
5, 15
5, 20
12, 21
15, 16
8, 30
12
10, 20
8, 30
15, 25
5, 20
14, 20
12, 25
10, 40
11, 15
10, 21
10, 15
7, 21
10, 12
5, 30
1, 10
4, 6
5, 25
5, 10
8, 23
13, 26
12, 20
10, 15
5, 24
12, 35
10, 20
7, 15
5, 15
5, 20
12, 21
15, 16
8, 30
13
10, 20
8, 30
15, 25
5, 20
14, 20
12, 25
10, 40
11, 15
10, 21
10, 15
7, 21
10, 12
5, 30
1, 10
4, 6
5, 25
5, 10
8, 23
13, 26
12, 20
10, 15
5, 24
12, 35
10, 20
7, 15
5, 15
5, 20
12, 21
15, 16
8, 30
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Scheduling Heuristic for STPs

• Known scheduling heuristic flexibility
• Amount of slack
• Planning phase
• assign action a to resource s.t. flex(a) is max
• Plan repair
• Choose action a s.t. flex(a) is min
• Move a to resource s.t. flex(a) becomes max

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Example (Gate Scheduling)

• Aircraft has delay can not dock before t50
• Inconsistency since flex value is negative
• Find gate with highest flex g2
• Move aircraft to that gate

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Conclusion

• Trying to bring together
• Multi agent system
• (temporal) Planning
• Scheduling aspects
• Application
• Collaborating with NLR (National Aerospace
  Laboratory)
• Extending airport simulator with MA tools

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Choices in STPs

• either action A before B or action B before A
• Disjunctive Temporal Problem
• MA voting protocol for decision making (BW,
  2004b)
• Reordering actions as a means of plan repair