You can take advantage of this option when you register your data feed in your account. Select the type of feed you're registering and then chose from a drop-down list of feed formats. We'll automatically format your feeds for proper integration and uploading into Google Product Search.
If you're an existing Google Product Search provider, please continue submitting your feeds in the Google Base format to take advantage of optional and custom attributes.
For more details and step-by-step instructions about uploading with alternative feed formats, please visit our Help Center article.
Posted by: Jessica Ng, Product Marketing Manager
Link - from Google Base Blog