5.3 Solution Plans 91
5.3 Solution Plans
In order to define planning algorithms in the plan space, we need to formally specify
what is a solution plan in the plan space. A solution plan for a problem P = (, s
0
, g )
has been formally defined, with respect to the semantics of state-transition systems,
as a sequence of ground actions from s
0
to a state in g (see Section 2.3.3). We now
have to take into account that actions in a partial plan π = (A, ≺, B, L) are only
partially ordered and partially instantiated.
A consistent partial order ≺ corresponds to the set of all sequences of totally
ordered actions of A that satisfy the partial order. Technically, these sequences
are the topological orderings of the partial order ≺. There can be an exponential
number ...