1. A computer-based method for representing and managing an inventory of advertising space that includes a plurality of advertising products and advertising impressions, comprising: by a microprocessor, running an inventory management module on a computer; by the inventory management module, generating a unique identifier for each of the advertising products within the inventory; wherein each of the advertising products comprise at least one attribute of a plurality of attributes and a corresponding attribute value; wherein the at least one attribute and corresponding attribute value of one or more of the advertising products has at least one attribute and corresponding attribute value in common with another one of the advertising products; by the microprocessor, processing input records associated with the advertising impressions; determining, by the microprocessor, for each of the processed input records, advertising products of the plurality of advertising products that match one or more attributes and corresponding attribute values of the input records and associating, by the microprocessor, each said input record with a representation of matching unique identifiers, and defining, by the microprocessor, an advertising product vector and a count of the advertising impression inventory associated with the advertising product vector; wherein the advertising product vector comprises a bitmap within which each bit corresponds to each one of the unique identifiers that defines the advertising products in the inventory; for the inventory, generating by the microprocessor a representation of the inventory as a plurality of inventory regions, wherein each inventory region is identified by the advertising product vector and its count defining a number of the advertising impressions corresponding to each of the inventory regions; storing the advertising product vectors and their counts; and in response to an inventory availability or forecast request being received by the inventory management module, providing a report that identifies a relevant portion of the counts for one or more of the advertising products in the inventory to a requesting device using the advertising product vectors.