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Reviewer 3.: how durative actions get assigned their starting and end times?

Note: from PDDL2.1 (Fox & Long 2003)

The modelling of temporal relationships in a discretised durative action is done by means of temporally annotated conditions and effects. All conditions and effects of durative actions must be temporally annotated. The annotation of a condition makes explicit whether the associated proposition must hold at the start of the interval (the point at which the action is applied), the end of the interval (the point at which the final effects of the action are asserted) or over the interval from the start to the end (invariant over the duration of the action).

Classically HTN planning define 3 kinds of trajectory decomposition constraints: before, after and between.
These three constraints are sufficient to express the preconditions at start at end and overall of a durative method.

In PDDL3.1 [other constraints] (https://www.cs.yale.edu/homes/dvm/papers/pddl-ipc5.pdf) exist see for details. Which constraints must be considered in HDDL2.1 ?

From Smith & Weld, 1999 (i.e. deterministic actions of fixed duration):

• The effects are realized at some unknown point during action execution, and thus can be used only once the action has completed.
• The preconditions must hold at the beginning of an action.
• The preconditions not be deleted by the action itself must hold throughout the duration of the action.

From PDDL2.1 Fox & Long, 2003:

• The preconditions may need to hold instaneously before the start (at start), before the end (at end) or over the complete execution of the action (over all).
• The effects are realized instantaneously either (at start) or (at end), i.e., at the beginning or the at the completion of the action (respectively).

From Mausam & Weld 2007:

• All executing actions terminate before the goal is considered achieved.
• An action, once started, cannot be terminated prematurely.

From Dvorák et al 2014:

• The action must always occur in the time interval of its parent action, its parameters are bound to the values defined in the parent, if any.

In order to avoid incompleteness (as for PDDL2.1), executing timepoints (epochs) i.e. time point when an action is allowed to start execution, must be allowed any time (or by defining time increments between actions(*) as defined by Haslum & Geffner 2001).

(*) The time to wait between the beginning of next action.

La effet négatif de l'action durative 26 (at end (not (on ?small_ship ?big_ship))) n'apparait pas dans les effet de l'action.

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