Search Spaces as a Unifying Theme

With a CBR system, the size of the space is all possible cases.
You solve a problem by retrieving a case, where you know the answer, that is close in the search space.
It's important that closeness is relevant to the solution.
What would happen if closeness weren't relevant?
Also ESs are good for problems with medium size search spaces
The shape of the search space is important in choosing the chaining mechanism for RBS.
The number of possible next states in each step can grow or shrink. If it grows, there's fan out, and if it shrinks there's fan in.
If there's fan in, you're going to have to choose between a small number of final states, so you want forward chaining.
If there's fan out, you're going to have to choose between a large number of final states, so you want backward chaining to, in essence, start at the goal final state and work backward.
You can also interleave chaining (do some forward and some backward chaining) to reduce the number of possibilities.