When you assign data masking rules to the data domain, the rules are called preferred rules. If you assign multiple rules to the data domain, you enable one of the rules to be the default rule. The default rule is applied to all columns in the data domain. You can manually change the masking rule for a column to a different preferred rule. You can also apply more than one masking rule to a column.

For example, an organization has a data domain called Last_Name. The Last_Name data domain describes columns that contain last names in company databases. The company can use a shuffle masking rule to mask the last names of customers in a database. The shuffle masking rule is the default rule. The organization applies a substitution masking technique to mask the last names of customers in a different table. The substitution masking rule is a different preferred masking rule in the data domain.