Cross-validation rules control combinations of values within a particular key flexfield structure. Cross-validation applies to combinations users attempt to create using either the combinations form or foreign key forms (using dynamic inserts).
Suppose you define a new cross-validation rule, but have existing entries in your combinations table that violate the rule. Since the existing combinations pre-date the rule, your flexfield continues to treat them as valid. However, if your end user tries to create a new combination that violates your new rule, your flexfield returns an error message and rejects the combination.
If you want to prevent users from using previously-existing combinations that are no longer valid according to your cross-validation rules, you can always manually disable those combinations using the combinations form. See: Maintaining Your Cross-Validation Rules and Valid Combinations.
By allowing dynamic inserts, you can let users create new combinations automatically upon entering the combination in a foreign key form (any form other than the combinations form) and in the combinations form itself.
If you want greater control, you can disallow dynamic inserts. You can thus restrict the creation of new combinations to certain authorized people who have access to the combinations form on their menu. You simply turn dynamic insertion off using the Define Key Flexfield Segments form. Depending on the key flexfield you use, you can still create new combinations using one of your product setup forms (the combinations form). For example, if you use the Accounting Flexfield, you can enter new combinations using the Define Accounting Flexfield Combination form.
In either case, however, there is no inherent protection against a user creating an invalid new combination. Cross-validation rules ensure that nobody can create invalid new combinations from either foreign key forms or the combinations form, regardless of whether you allow dynamic inserts.
As you consider the controls you want over your key flexfield combinations, determine whether you need cross-validation rules at all. To provide an extra level of security, use cross-validation rules even if you turn dynamic insertion off. This allows you to double-check new combinations that even your authorized personnel enter using the combinations form.
Key Flexfield Segments Window
Cross-Validation Rules Window
Maintaining Your Cross-Validation Rules and Valid Combinations
Defining Cross-validation Rules
Defining Cross-validation Rule Elements