Unless you are participating in Product Ratings through Google Customer Reviews, you will need to provide a feed if you would like to display product reviews and ratings. This article explains how to properly format your Product Ratings feed.
Note that providing a feed does not guarantee that your content will be included on Google. Your reviews must always comply with our program policies.
An XML schema gives guidance on how to structure the XML feed and uses the .xsd file extension. The XML schema for Product Ratings is published here.
Please refer to the Google Developers' site for more detail on the Product Ratings XML schema and feed organization.
To ensure that Google can process your feed, please use an XML schema validator before submitting your feed.
For more information on validating your feed, visit the XML Validation page on the Google Developers' site