Currently, tag service is associated with a security zone if and only if any service-resource (that is, a tuple <resource-service, resource> ) in the Security Zone is contained in resource-service that is associated with the tag service. However, consider the following use case:
1) No zone exists. Tag-based policies are in-place, say for PII, EXPIRES_ON, etc.
2) Few tables in finance DB were tagged with EXPIRES_ON; few columns within this DB were tagged with PII. So tag-based access enforcement/masking policies are in effect for these objects.
3) An admin creates 'Finance' zone and moves 'finance' DB to this zone.
4) All tag-based policy enforcement is lost; as there is no tag-based policy in 'finance' zone, as the policies still belong to “unzoned” zone.
Given this, it is a better design to not automatically create tag-service->zone association. Instead, the association between zone->tag-service needs to supported directly similar to how zone->resource-service association is established, with one difference; when a tag service is associated with a Security Zone, user should not be able to include any resource (tag-name, to be specific). This requires GUI changes for Security Zone CRUD, but no other changes, especially to tag service browser as well as tag policy creation.
On the access evaluation perspective, if accessed resource falls in a Security Zone, then there are two cases:
1) Tag-service associated with the Resource-service is in the Security Zone.
2) Tag-service associated with the Resource-service is not in the Security Zone.
Tag policies in associated Tag-service in the default ("unzoned") Security Zone need to be considered for evaluation in case 2.