protected void RemoveRule(DataModelValidationRule rule)
{
DebugCheck.NotNull(rule);
Debug.Assert(_rules.Contains(rule), "should exist");
_rules.Remove(rule);
}
protected void AddRule(DataModelValidationRule rule)
{
DebugCheck.NotNull(rule);
Debug.Assert(!_rules.Contains(rule), "should not add the duplicate rule");
_rules.Add(rule);
}