When introducing a system, we have seen cases where it took more man-hours and cost more than expected to build the interface. We have seen cases where the construction of the interface took more man-hours and cost more than expected when introducing a system. In many cases, interfaces must be built at a cost of tens of millions of dollars when connecting multiple systems on a large scale. This document summarizes points to consider when building an interface that you should know before selecting a project revenue management system.