A Liquid Narrative Group System

Longbow is a hierarchical discourse planning system that combines decompositional reasoning (planning to perform an abstract action by performing that action’s substeps) and causal reasoning (planning to perform an action by ensuring that the action’s preconditions all hold before its execution) in the same representation.

The Longbow system is based on a domain-independent hierarchical AI planning algorithm named DPOCL (Decompositional, Partial-Order Causal Link planner) which itself is built on top of a non-hierarchical planner, UCPOP. Longbow differs from DPOCL and UCPOP by containing extensions that make representing communicative actions possible.

Highlights of Longbow’s Feature List include:

• Longbow’s extended plan representation includes:
  • the intentional and informational structure of a discourse, represented in a clean and precise manner.
  • communicative actions with multiple effects.
  • tree-structured plans as well as graph-structured plans (that is, discourse plans that share components between distinct segments).
  • plans with interleaved subplans (that is, discourse plans that interleave communicative actions from distinct segments).
  • a flexible recipe-writing language allowing the operator writer to specify complete recipes, empty recipes or partial recipes.

• Longbow’s planning algorithm provides:
  • reasoning that combines hierarchical and causal planning.
  • a plan-space search function, making debugging more straightforward.
  • a provably sound and complete planner.
  • the ability to include user-defined and domain-specific search-control knowledge distinct from the planning algorithm.
  • easy integration with external knowledge bases.
  • graphical user interfaces being developed for CLIM 2.0 and the Macintosh Common Lisp and ACL/PC user interface packages.

Team members

• R. Michael Young (faculty contact)

Longbow publications

Young, R. Michael, Martha E. Pollack and Johanna D. Moore, Decomposition and causality in partial-order planning, Intelligent Systems Program Technical Report 94-2, University of Pittsburgh, 1994.

Young, R. Michael. A Developer’s Guide to the Longbow Discourse Planning System, Intelligent Systems Program Technical Report 94-4, University of Pittsburgh, 1994. [PDF]

Young, R. Michael and Johanna D. Moore, (1994) Does Discourse Planning Require a Special-Purpose Planner? In the proceedings of the AAAI Workshop on Planning for Inter-Agent Communication, Seattle, WA, 83-90. [PDF]

Young, R. Michael and Johanna D. Moore, DPOCL: A principled approach to discourse planning, inProceedings of the Seventh International Workshop on Natural Language Generation, Kennebunkport, ME, pages 13-20, July, 1994. [PDF]

Young, R. Michael, Martha E. Pollack and Johanna D. Moore, Decomposition and causality in partial-order planning, in Proceedings of the Second International Conference on AI and Planning Systems, Chicago, IL, pages 188-193, July, 1994. [PDF]

Young, R. Michael, Johanna D. Moore and Martha E. Pollack, Towards a principled representation of discourse plans. In Proceedings of the Sixteenth Annual Meeting of the Cognitive Science Society, Atlanta, GA, pages 946-951, August, 1994. [PDF]

Longbow sponsors

The US Office of Naval Research