When requirements analysts are thorough, those who read and use the requirements can easily get lost in the muck and mire of the details. I have found that diagrams can add much more specificity to requirements than lengthy narratives describing business rules. This diagram depicts a small excerpt from a requirements model of a financial system.

This tiny drawing eliminates the need to write out all of the following business rules, because they are all clearly shown in the model:

  • Every account must be associated to one customer.
  • An account cannot be associated to more than one customer.
  • An account cannot exist if it does not have a corresponding customer.
  • A customer must have at least one account.
  • A customer may have more than one account.
  • An account must be either an individual account or a corporate account.

Some restrict the use of drawings like this for design, others argue that domain models are old school. I have had great success using this approach for describing business rules. The economy of words eliminates ambiguity, is much more thorough, and can be easier for a designer/developer to use when designing a solution.