1. A data processing system comprising: a CPU; a computer-readable memory storing a data structure, the data structure comprising a database of market research information, the data structure including: current information related to a market aspect of products, wherein the current information is current in time, and wherein the current information includes a first historical control designator identifying the current information as being current in time; and, previous information related to the market aspect of products, wherein the previous information is previous in time to the current information, and wherein the previous information includes a second historical control designator identifying the previous information as being previous in time to the current information; wherein one of the first and second historical control designators is unique.