19.6 The Deep Space 1 Experiment 461
Plans. In DS1, plans are special cases of chronicles, as described in Chapter 14.
Candidate plans are refined incrementally by the planner until they are a solution
for the given goal. A candidate plan contains the following elements.
•
A horizon (h
s
, h
e
) represents the time window considered by the plan.
•
A set of timelines, i.e., sequences of tokens (T
1
, ..., T
k
), contains one token
for each state variable x, with T
i
= (x, p(y
1
, ..., y
m
), s
i
, e
i
).
•
Ordering constraints enforce that each token in the sequence is followed by
the next token, i.e., h
s
≤ s
1
≤ e
1
≤ s
2
≤ ... ≤ e
n−1
≤ s
n
≤ e
n
≤ h
e
.
•
A set of equality and temporal constraints enforces required conditions.
The Search Engine. SE starts from an initial candidate plan, ...