1. A computer system for building an inventory database, the computer system comprising: an electronic memory storage configured to store modules; a computer processor configured to execute the modules comprising at least: a data access module configured to access inventory data for a plurality of products from at least one inventory data source, a metadata extractor module configured to extract stated metadata from the inventory data for each of the plurality of products, wherein stated metadata comprises attributes of a product that are obtained from a product description provided by advertisers or suppliers of the plurality of products in the inventory database, a product evaluator module configured to determine a product category or a product identification based on the stated metadata for each of the plurality of products, a comparator module configured to compare for each of the plurality of products the product category or the product identification to stored metadata in a metadata database, wherein the metadata database comprises additional metadata for a plurality of products, a metadata identifier module configured to identify derived metadata for each of the plurality of products based on the comparison, wherein the derived metadata comprises attributes of a product that are identified based on characteristics of the product and that are not stated in a product description provided by advertisers or suppliers of the plurality of products in the inventory database, and wherein the derived metadata is stored in the metadata database, a conversions module configured to generate a specific conversion rate for each of the plurality of products based on inputting the stated metadata and the derived metadata into a conversion rate formula, wherein the specific conversion rate relates to generating more click-throughs or higher revenue, and wherein the conversion rate formula is based on a linear or logistic regression analysis, a conversion rate assignor module configured to assign the specific conversion rate corresponding to each of the plurality of products, and a storage module configured to store in the inventory database for each of the plurality of products the stated metadata, the derived metadata, and the specific conversion rate.