There are many ways to design a knowledge base, and you are free to design your knowledge base as you like, but it should be expressed in terms of facts and rules. For example, you can design the problem in terms of a state space search with an initial value for the tuple $($Farmer$,$ Goat, Cabbage, Wolf$)$ and a goal state to reach. The initial state represented in terms of fact would be state $($e$,$ e$,$ e$,$ e$),$ which means that all items are on the east shore of the river. The goal state will then be state $($w$,$ w$,$ w$,$ w$).$ Each rule will represent a possible move, and when the rule is fired it will change the value of the state until it reaches the goal state $($w$,$ w$,$ w$,$ w$).$