Last modified: Wed May 1 11:19:46 1996
- This category includes systems
such as STRIPS [Fikes and Nilsson 1971],
HACKER [Sussman 1975], NOAH
[Sacerdoti 1977] and
MOLGEN [Stefik 1981a, Stefik 1981b]. Recent
classical planners include TWEAK
[Chapman 1987], SNLP [McAllester and Rosenblitt 1991]
and UCPOP [Penberthy and Weld
1992]. The term
is due to Wilkins .
- Cassandra was a Trojan prophet
who was fated not to be
believed when she accurately predicted future disasters. An earlier
version of Cassandra was described in [Pryor and Collins 1993].
- Appendix A shows the plans that
constructs for all the examples described in this paper. This plan
is in Section A.1.
alternative method would be to split the plan into two branches,
regardless of the number of outcomes. In this case, one branch
would be associated with a given outcome of the uncertainty, while
the other would be associated with all other possible outcomes of
that uncertainty. This is effectively how SENSP operates
[Etzioni et al. 1992].
that we are describing the contingency in this way for clarity of
exposition. The actual label is constructed as described in
- Assuming that ?U, the variable representing the
source of uncertainty, is instantiated to U1.
obvious extension to Cassandra would be the construction of a
post-processor that spots decision-rules that do not discriminate
between particular sets of outcomes, and prunes the plan to remove
superfluous contingencies. Note that it cannot be determined until
the plan is complete whether such a condition pertains.
- This raises the obvious
question as to whether
planning in advance for every possibility is a sensible thing to do.
See Section 7.4 for a
discussion of this issue.
- Neither NOAH
[Sacerdoti 1977] nor Interplan [Tate1975] explicitly addressed
issues of uncertainty, although both tackled problems involving it
[Collins and Pryor1995].
- See Section 8.2 for
further discussion of this issue and an alternative approach.
- Not all agents can make use of this
information, as there is no guarantee that the third type of step
will actually be executable.