Case-based Planning with a High-Performance Parallel Memory
Case-based Planning with a High-Performance Parallel Memory
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Date
1998-10-15
Authors
Kettler, Brian
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Abstract
Case-based planning (CBP) systems, like other case-based reasoning
systems, can take advantage of previous planning experience by reusing
stored cases (plans) in similar situations in the future. Advantages
of CBP include speedup over planning from scratch and the ability to
function with limited causal domain knowledge. ``Traditional'' CBP
systems with the latter advantage typically cannot produce plans from
scratch because they lack the more powerful adaptation mechanisms of
generative planning systems. These ``reuse-only'' CBP systems rely on
retrieving a plan from the casebase that is close to a solution plan.
This requires large casebases with good coverage of the problem space
and the ability to encode and match cases at fine levels of detail.
Many such CBP systems, however, have fallen short of these
requirements. They support only small, pre-indexed casebases.
Pre-indexing constrains retrieval, as does the use of less expressive
feature-based case representation schemes. The encoding and matching
of detailed structural relationships in cases is not possible in such
systems. These systems often adapt a single plan to the target
problem using methods that are ad hoc or heuristic.
CAPER is a novel, domain-independent, case-based planning system with
improvements over traditional reuse-only CBP systems from its use of
techniques that exploit a high-performance parallel memory of cases.
CAPER takes a memory-intensive approach by making frequent use of
memory during all phases of planning and by using large casebases,
which can be automatically seeded. Because the parallel retrieval
mechanisms scale to real-world sized casebases of thousands of plans,
memory does not have to be pre-indexed and thus retrieval is more
flexible. Detailed queries can be used to match cases, which are
stored using an expressive, graph-structured case representation
scheme.
Plan adaptation in CAPER borrows techniques from generative planning,
such as the use of plan validations, which capture dependencies in a
plan, and plan composition. These techniques are incorporated into a
reuse-only CBP framework for a more principled approach to adaptation
than in many reuse-only CBP systems. CAPER can also use its flexible
retrieval mechanisms and case representations to retrieve patch or
substitute plans from memory.
(Also cross-referenced as UMIACS-TR-95-112)