This documentation describes which Attributes are required, suggested, or optional for structured data with special intending to Google Lookup. Most Look for structured facts uses schema.org vocabulary, but it is best to rely on the Google Research Central documentation as definitive for Google Lookup actions, in lieu of the schema. https://getsocialselling.com/story4026223/the-fact-about-product-schema-example-that-no-one-is-suggesting