1. A method comprising: using a computer, identifying a hierarchy of products, each product in the hierarchy having known attributes, wherein the hierarchy of products includes blocks of products defined by values of one or more block attributes of the products in the block; receiving a record of attributes of an unclassified item, the record including block attributes and match attributes of the unclassified item; and assigning a block location in the hierarchy to the unclassified item, based on probabilistic matching among the block attributes of the products in the hierarchy and at least one known block attribute of the unclassified item, and then assigning a location within the block to the unclassified item, based on probabilistic matching among the match attributes of the products in the block location and at least one known match attribute of the unclassified item, thereby classifying the item.