Can two planning PDDL actions be taken simultaneously?

Question

We are discussing planning algorithms currently, and the question is to describe the steps to check if actions could be taken simultaneously. This is a really open-ended question so I'm not sure where to start.

Answer 1

First place to look is how the preconditions/effects of different actions interact.

Answer 2

I don't see any principal problem with that. The way I would approach it is to have a resource model and durations attached to actions.

For example, movement would put a lock on your legs. You can't have another movement at the same time, as your legs are already busy. But your attention might only be partially occupied, so you can make a phone call while you're moving. You won't be able to read a book, because your eyes might be partially busy monitoring the walking action. This can be encoded in pre- and post-conditions.

What will probably be easier is to parallelise the execution of the plan. Once the plan has been created, organise the actions in a Gantt-chart like structure. You can have mutual exclusion in there, so all 'movement' would be restricted to one single row, so no more than one movement can take place at the same time. But 'making a phone call' could be in a separate row, and thus execute in parallel. The details depend on the requirements of the actions.

I can't easily think of a way that it would impact the planning process itself; unless there are critical timings involved. So leaving the planner to do its thing might keep it simpler, and then the optimal execution could be a post-processing step.