Adding Intervals to Temporal Planning

[uwe-koeckemann]

User Story

As a Timeline-based Planner Provider I want to access implicit or assign explicit intervals to preconditions, effects, actions, states, and goals to impose temporal (and resource) constraints between these intervals.

Acceptance Criteria

• [ ] Implicit interval handles can be obtained for any precondition, effect and action, as well as any goal or state expression
• [ ] Explicit intervals can be attached to any precondition, effect and action, as well as any goal or state expression
• [ ] Constraints using temporal intervals can be added to problems or actions

Additional Material

• Suggestion below is based on discussion #45

import upf

Location = upf.UserType('Location')
robot_at = upf.Fluent('robot_at', BoolType(), [Location])
distance = upf.Fluent('distance', RealType(), [Location, Location])

move = upf.DurativeAction('move', l_from=Location, l_to=Location)
l_from = move.parameter('l_from')
l_to = move.parameter('l_to')

i_move_1 = Interval('C1')
# or: i_move_1 = 'C1_
# similar for other intervals used below ...

# Intervals may be attached as optional arguments:
move.set_duration_constraint(IntervalDuration(5, 16))
move.add_start_condition(Not(Equals(l_from, l_to)), delay=3) 
move.add_condition(StartTiming(), Not(Equals(l_from, l_to)), interval=i_move_1)
move.add_condition(EndTiming(3), robot_at(l_from), interval=i_move_2)
move.add_condition(EndTiming(), Not(robot_at(l_to)), interval=i_move_3)
move.add_effect(StartTiming(), robot_at(l_from), False, , interval=i_move_e_1)
move.add_effect(EndTiming(),robot_at(l_to), True, interval=i_move_e_2)
move.add_durative_condition(LeftOpenInterval(StartTiming(), EndTiming()), Not(robot_at(l_to))) 

i_move = Interval()
move.set_interval(i1)

# add a temporal constraint:
move.add_constraint(Duration(i_move, 10, 20)) # flexible duration
move.add_constraint(Meets(i_move_2, i_move_e_2)) # relate condition and effect
move.add_constraint(Overlaps(i_move_2, i_move)) # relate precondition and action

# attach a resource usage to an interval
r1 = ReusableResource(capacity=1)
move.add_constraint(Use(r1, 1, interval=i_move)

# access condition interval based on add_condition order?
i_move_1_alt = move.get_condition_interval(0) 
assertEquals(i_move_1_alt, i_move_1)

l1 = upf.Object('l1', Location)
l2 = upf.Object('l2', Location)
problem = upf.Problem('robot')
problem.add_fluent(robot_at)
problem.add_durative_action(move)
problem.add_object(l1)
problem.add_object(l2)
problem.set_initial_value(robot_at(l1), True, interval=Interval())
problem.set_initial_value(robot_at(l2), False)
problem.add_timed_effect(100, AssignEffect(robot_at(l2), False))
problem.add_goal(robot_at(l2), interval=Interval()) # At the end of the plan robot is in l2
problem.add_timed_goal(500, robot_at(l1)) # At time 500 robot is in l1
problem.add_maintain_goal(LeftOpenInterval(50, 100), robot_at(l1)) # Between (50 and 100] robot stays in l2

Attention Points

• Intervals must be grounded to unique instances in a ground action (e.g., many instances of a move action in the same plan must use unique intervals)
  • Intervals of preconditions/goals may be substituted by effect/state intervals that provide them, but this is the same as using unique names and a temporal equality constraint between them.
• Once an interval is grounded/instantiated for a concrete action, it can be used to relate multiple actions in a temporal plan
• (Maybe this should be a discussion instead. Let me know and I'll move this over.)

[alexander-sung]

I'd like to add to the relevance of this issue since I'm currently trying to model a problem which has certain fluents set to specific values in some intervals in the future. My understanding is that problem.set_initial_value(robot_at(l1), True, interval=Interval()), as an example, is addressing this.

Additionally, is mentioning actions in the user story also covering actions already being executed at planning time? Referring to the example from https://colab.research.google.com/github/aiplan4eu/unified-planning/blob/master/notebooks/Unified_Planning_Temporal.ipynb, let's say I'm executing the first plan received for 3 seconds but then notice one of the planned matches is broken and I need to replan to use another. At this point in time I would like to specify that one match is already in use, thus giving light. On the other hand, a fuse is currently being mended, so that hand is not free. Instead of reproducing all the actions' effects, it would be convenient to specify actions already being executed. Is this covered here? Otherwise I would create a separate user story, no problem. Let me know in case that's preferred. Thanks.

[mikand]

@uwe-koeckemann Closing this for now: we do have some interval support in temporal and hierarchical planning, but no engines generally support very expressive interval reasoning (at least for now...)