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Attributes with the exact same name (case sensitive) are auto-mapped. Furthermore it is not necessary to map all attributes. You can also edit the mappings later when clicking on the "Properties" button in the control bar.
Confirming this dialog adds your product data to your Product Guide.
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Read our FAQ regarding Product Data to learn when uploaded product data is live in the Product Guide, or how to combine changes/adaptations in your Product Guide and in your product data at the same time.