# Mapping table > An integrator's table linking canonical SKUs to PhotoRobot item IDs and external IDs. Category: E-commerce and workflow. A mapping table links identifiers of the same object across systems. It is usually a database table owned by the integrator. ## How PhotoRobot uses it In a PhotoRobot integration it connects the [canonical SKU](https://www.photorobot.com/glossary/sku-canonicalization), the PhotoRobot item ID and the [external ID](https://www.photorobot.com/glossary/external-id), with indexes for duplicate checks, webhook lookups and the status round-trip. Covered in module [I03](https://www.photorobot.com/academy/curriculum#i03-shooting-list-sku). ## Related terms - [SKU canonicalization](https://www.photorobot.com/glossary/sku-canonicalization): Normalizing product codes to one form before matching, so one product never becomes several items. - [External ID](https://www.photorobot.com/glossary/external-id): The customer's own product identifier stored with a PhotoRobot item, for syncing status back. - [Status round-trip](https://www.photorobot.com/glossary/status-round-trip): Sending an item's status from PhotoRobot back to the upstream ERP through a webhook.