Dual views of HTN planning
Capturing hierarchical structure of the domain
- Motivates top-down planning
- Start with abstract plans, and reduce them
Many technical headaches
- Respecting user-intent, maintaining systematicity and minimality [AAAI-98]
- Phantomization, filters, promiscuity, downward-unlinearizability..
Capturing expert advice about desirable solutions
- Motivates bottom-up planning
- Ensure that each partial plan being considered is “legal” with respect to the reduction schemas
Connection to efficiency is not obvious
Relative advantages are still unclear...