7.11. Commentary: Domain Rules
Domain rules [Ross97, GK00] dictate how a domain or business may operate. They are not requirements of any one application, although an application's requirements are often influenced by domain rules. Company policies, physical laws (such as how oil flows underground), and government laws are common domain rules.They are commonly called business rules , which is the most common type, but that term is poor, as many software applications are for non-business problems, such as weather simulation or military logistics. A weather simulation has "domain rules," related to physical laws and relationships, that influence the application requirements.It's useful to identify and record domain rules in a separate application-independent artifactwhat the UP calls the Business Rules artifactso that this analysis can be shared and reused across the organization and across projects, rather than buried within a project-specific document.The rules can help clarify ambiguities in the use cases, which emphasize the flow of the story rather than the details. For example, in the NextGen POS, if someone asks if the Process Sale use case should be written with an alternative to allow credit payments without signature capture, there is a business rule (RULE1) that clarifies whether this will not be allowed by any credit authorization company.