Factual knowledge includes the concept base, the instance base, and the relations among them. Subgoals that arise during problem solving are solved by methods. Some method bodies are calls to Lisp functions that are executed without further subgoaling. The upper part of the picture shows factual knowledge that is domain independent and can be reused for any domain. The state is described with a set of variables.
Constraints can have fixes.
In a configuration problem, the state is a configuration. Some of the state variables denote components, i.e., pieces of equipment that together form a configuration. A component may have an upgrade, e.g., a more powerful model of that kind of equipment. The lower part of the picture shows factual knowledge that is relevant only to the U-Haul domain. One of the state variables denotes the equipment that the client can rent, which can be a trailer, a rooftop, or a truck.