Tool Support for Planning and Plan Analysis within Domains embodying Continuous Change

1. Tool Support for Planning and Plan Analysis within Domains embodying Continuous Change Lee McCluskey and Ron Simpson University of Huddersfield Informatics Research Group University of Huddersfield

2. Contents • The Message • Review of GIPO III with classical domains • GIPO III with continuous domains • Experimental HTN Planner for PDDL+ • The Message again.. Informatics Research Centre University of Huddersfield

3. Message Using the object metaphor successfully allows the GIPO software platform to provide (to some extent) • domain independent and • planner independent graphical means to do acquisition/formulation/analysis of domain models … We postulate that the object metaphor can be used effectively to help analyse and manage plans independent of domains/planners in classical and non-classical (eg continuous) domains Informatics Research Centre University of Huddersfield

4. Background: GIPO III • GIPO family - Graphical Interface for Planning with Objects is a tools environment (implemented in Java) to help in the construction of bug-free domain models. • GIPO tools includes consistency checkers, a diagrammatic PDDL-generating interface (the OLHE), a plan stepper, a plan animator, inbuilt planners, an interface to third party planners, an operator induction technique, a random task generator etc Informatics Research Centre University of Huddersfield

5. GIPO – versions GIPO 1 Generally available For ‘Flat’ models (ECP’01) GIPO 2 + automated induction of action schema (AIPS’02) + HTN represntation (ICAPS’03) GIPO 3 + OLHE + Cts domains ICKEPS award (ICAPS’05) Informatics Research Centre University of Huddersfield

6. GIPO Demonstration Example: Lazy Hiking World • Imagine Sue and Fred want to have a hiking holiday in the Lake District in North West England. • They walk in one direction, and do one ``leg'' each day. But not being very fit, they use two cars to carry them / the tent / their luggage to the start/end of a leg. • They must have their tent up already so they can sleep the night, before they set off again to do the next leg in the morning. • Actions include walking, driving, moving and erecting tents, and sleeping. • The requirement for the planner is to work out the logistics and generate plans for each day of the holiday. Fairfield Helvelyn Coniston Informatics Research Centre University of Huddersfield

7. GIPO demo 1 Informatics Research Centre University of Huddersfield

8. OCL+ OCL+ is an object-centred form of PDDL+ • Actions/operators bring about instantaneous change to the state of domain objects and may also update the numeric properties of objects • processes are automatically triggered when the current state matches their start condition; they specify how the numeric properties of the objects in the domain are updated with the passage of time • events are automatically triggered as a result of the numeric changes brought about by domain processes; events bring about instantaneous state change and may also update numeric properties of the objects of the domain. • OCL+ has continuous variables, with ‘test’ functions in preconditions and ‘assign’ functions in postconditions Informatics Research Centre University of Huddersfield

9. GIPO demo 2 Informatics Research Centre University of Huddersfield

10. Another example - Air Traffic Control ATC can use the simulation to do a ‘conflict probe’. In the event of a violation, the controller can add actions to the plan and re-run it Informatics Research Centre University of Huddersfield

11. PlusPlan GIPO has HyHTN – a hierarchical “hybrid” planner – usese: HTN decomposition AND state space search, using plan-graph heuristic plan generation. PlusPlan is derived from HyHTN and attempts to do planning in continuous domains Informatics Research Centre University of Huddersfield

12. PlusPlan Plus Plan Algorithm (more details in paper) • Repeat • expand open plans • simulate events and processes • Until no open plans left or we have a solution • Expand open plans: for each open plan P.. • Decompose methods in P • Apply applicable operators in P • Until run out of open plans • Simulate events and processes: • for all executable events, execute them • for all processes, execute them (incrementally) Informatics Research Centre University of Huddersfield

13. Discussion - Instantaneous Events Once time is continuous, two main problems: • approximation of time • Instantaneous events and actions happening at the same time Events and Actions instantaneously change states of objects. This leads to the problem - • they can occur at the same instant if the preconditions of an event and an action can be true in a valid state. What happens if the effects interfere? Informatics Research Centre University of Huddersfield

14. Discussion - One solution is to make sure this is not the case for domain models - but this may lead to unnatural encodings.. • GIPO’s choices: -- ask the user to provide the granularity for time (not implemented yet!) -- enforce an ordering: Actions > Events > Processes at each instant of time Informatics Research Centre University of Huddersfield

15. Conclusions – that message again Using the object metaphor successfully allows the GIPO software platform to provide (to some extent) • domain independent and • planner independent graphical means to do acquisition/formulation/analysis of domain models … We postulate that the object metaphor can be used effectively to help analyse and manage plans independent of domains/planners in classical and non-classical (eg continuous) domains Informatics Research Centre University of Huddersfield