This states that a particular gr:ProductOrServiceModel is a variant of another product or service model. It is pretty safe to infer that the variant inherits all gr:quantitativeProductOrServiceProperty, gr:qualitativeProductOrServiceProperty, and gr:datatypeProductOrServiceProperty values that are defined for the first gr:ProductOrServiceModel. Example: foo:Red_Ford_T_Model gr:isVariantOf foo:Ford_T_Model