Hybrid not implemented in POM2 --

The hybrid sorting policy of POM1 was not implemented in POM2 due to questions regarding the "fairness" and consistency of the hybrid implementation with respect to the other sorting algorithms.

One concern regarding the hybrid sorting policy in POM1 is that it has the ability to end an iteration early when remaining requirements do not meet a minimum cost-benefit criteria. When a hybrid iteration is ended early, the remaining budget for that iteration is carried over into the next iteration and new requirements along with the existing requirement value changes are immediately known. This allows hybrid to put off requirements until later in the process when more requirement information is known, thus allowing more accurate planning. With no penalty for pushing back requirements and no limitation on budget carryover, the optimal solution would be to put off all requirement until the final iteration before executing the entire budget.

Also, while the cost of implementing a sorting policy has not been quantified and implemented in the scoring, it should be noted that the hybrid sorting policy has much more overhead than the other policies. Essentially, it is the best of both plan-based and agile in terms of sorting. The hybrid sorting policy can see all requirements and sort all requirements inititally, like plan-based, but it can also sort the plan each iteration like agile. Therefore the cost of implementing a hybrid sorting policy would certainly be more costly than either plan-based or agile.

For these reasons, we felt it best to not implement a hybrid sorting policy for POM2 and instead focusing the more readily comparable sorting policies of plan-based and agile.