In addition to domain values, there is a need to add business rules to each domain or combination of domains. DQS supports the adding of domain rules. The rule can be something like checking if the value is greater than something or matching with a regular expression and so on. Rules can also be applied on multiple domains in a composite domain; CD rules are helpful when providing business rules for the relationship between multiple domains, for example, a female or male title based on their marital status.