Many Rules

• Structured programming languages largely specify the order that statements will be executed.
• Rule based systems by default do not.
• This is the power and problem with them.
• You can of course arrange it so that they are applied largely in the order you want.
• One mechanism would be to have a program-counter fact, and each rule would have a different value on the if side, and would change the value on the then side to select the next rule to apply.
• This requires the programmer to select which rule to come next and largely erases the simplicity of a rule based system.
• However, you can reach a happy medium.
• You largely leave the system to choose which rule to apply next, but in certain cases you manage it.
• The three basic control structures are branching (e.g. if then else), looping, and function calls. You can do them all with rules.