A project portfolio management system creating virtual interrelationships between projects. Aspects of the system include creating virtual relationships at the Work Breakdown Structure (“WBS”) level with appropriate offsets using interpretations of logic relationships in detailed project schedules using various calculation approaches. The system models the linkages between detailed project schedules in a virtual relationship usable in alternate scenario planning analysis at a summary or working level. The virtual relationships are accurate enough for high level planning by users (e.g., program managers and analysts) with limited familiarity of project details (e.g., which non-workdays are in which project calendars) and reduce the computation times when altering a project planning scenario. Using the virtual relationships allows scenarios to be quickly evaluated to gauge the effects of changing constraints before committing to recalculating the detailed schedules of a project.