What is the difference between a world state and a state description and a search node and Why is this distinction useful?

Answer 1

A world state is how reality is or could be. In one world state we’re in Arad, in another we’re in Bucharest. The world state also includes which street we’re on, what’s currently on the radio, and the price of tea in China. A state description is an agent’s internal description of a world state. Examples are In(Arad) and In(Bucharest). These descriptions are necessarily approximate, recording only some aspect of the state.

We need to distinguish between world states and state descriptions because state description are lossy abstractions of the world state, because the agent could be mistaken about how the world is, because the agent might want to imagine things that aren’t true but it could make true, and because the agent cares about the world not its internal representation of it.

Search nodes are generated during search, representing a state the search process knows how to reach. They contain additional information aside from the state description, such as the sequence of actions used to reach this state. This distinction is useful because we may generate different search nodes which have the same state, and because search nodes contain more information than a state representation.