What information is necessary to encode about the the world to sufficiently describe all relevant aspects to solving the goal?

That is, what knowledge needs to be represented in a state description to adequately describe the current state or situation of the world?

By making this decision, theknowledge engineer decides what features of the world are needed. This keeps the system from considering irrelevant aspects of the environment.

 The size of a problem is usually described in terms of the number of states that are possible. For example, in Tic-Tac-Toe there are about 3^9 states. In Checkers there are about 10^40 states. Rubik's Cube has about 10^19 states. Chess has about 10^120 states in a typical game.

 We will use the Closed World Assumption: All necessary information about a problem domain is available in each percept so that each state is a complete description of the world. There is no incomplete information at any point in time.