The Notion of State

A declarative model that is good for describing control logic is based on the notions of state and state transition. The state of a system is a summary of its history, and the state transition function describes how the state changes with input.

Here are some examples of state and state transition:

state	input	state transition
values in computer memory	instructions	assign new values to variables
your net worth	income and expenditures	changes when you save or spend
parking meter flag and timer positions	clock tick and coin insertion	changes with passage of time and coin insertion
customers present in a store	customers enter or leave	changes when customers enter or leave store
positions and velocities of masses	forces	positions and velocities are changed according to Newton's laws

For some of these, the state changes discretely in response to discrete input events. We will focus first on such examples.

Week 3

The Notion of State