Metadata-driven processing of supplemental data feeds

A metadata-driven merchant feed processing system is described herein. A merchant providing an online marketplace for the sale of items by a variety of sellers implements a feed processing mechanism driven by feed metadata. The feed metadata consists of declarative metadata statements that model the semantics for transforming seller-facing feed data describing the seller's items to customer-facing listings data to be loaded to an item catalog. The feed metadata captures differences between different versions of the item catalog by maintaining the semantics of the product categories and attributes of the item catalog as of a certain version. Similarly, semantics in the feed metadata modeling new product categories and/or attributes are utilized to support supplemental feeds from sellers to support new features and improvements in the item catalog. The metadata driven feed processing system also provides support for multiple types of seller-facing data entities and feed formats through metadata mapping.