Collection of strategies presented so far can reason either forward or backward, but for a given problem, one direction or the other must be chosen.
A mixture of the two directions is appropriate. Such a mixed strategy would make it possible to solve the major parts of a problem first and then go back and solve the small problems that arise in “gluing” the big pieces together.
The technique of Mean-Ends Analysis (MEA) allows us to do that.
MEA process centers around the detection of differences between the current state and goal state.
Once such a difference is isolated, an operator that can reduce the difference must be found.
If the operator cannot be applied to the current state, we set up a sub-problem of getting to a state in which it can be applied.
The kind of backward chaining in which operators are selected and then sub-goals are set up to establish the preconditions of the operators is called operator sub-goaling.
