Decision modelling dramatically changed how I view business rules. In a nutshell, business rules are not particularly useful on their own. For example, if the business has a rule that a person must be aged 18 or over in order to have an account, that does not give us the full picture. What decision is the business trying to make when taking into account a person’s age? What other data (fact types) does the business take into account when making that decision? At which points in which processes can that decision be made? What other decisions take into account a person’s age?