1. A message prioritization process comprising: an interface process for receiving a primary attributable security interest message and one or more secondary attributable security interest messages placed by the market participant on a securities trading system, wherein the primary attributable security interest message relates to a defined quantity of an individual security traded on the securities trading system, and each secondary attributable security interest message increments the defined quantity of the primary attributable security interest message by an incremental quantity; and a code assignment process for assigning a superior prioritization code to the primary attributable security interest message and an inferior prioritization code to each secondary attributable security interest message; wherein the prioritization codes control the order in which the attributable security interest messages are processed by a matching process, and the inferior prioritization code is subordinate to the superior prioritization code.