Ranking rules:

Levelling resources to minimize the maximum amount of resource needed at any point in time is a very difficult combinatorialy explosive problem, so it is solved via heuristics. A single project may require a variety of different resources, or many different projects may complete for one or more resources. Heuristic methods are generally used to modify schedules obtained by the conventional means. Several heuristic methods involve ranking activities according to some criterion and resolving conflicts according to the sequences of ranking. Some of the ranking rules are as follows:

Minimum Job Slack

Priority is given to activities with the smallest slack

Latest Finishing Times

While resource conflict exists, this rule assigns priority to the activity with the minimum latest finishing time.

Greatest Resource Demand

This rule gives priority on the basis of the total resource requirements of all kinds, giving highest priority to the activities having greatest resource demand. The rationale behind this method is to give priority to potential bottleneck activities.

Greatest Resource Utilization

This rule gives priority to that combination of activities that result in the maximum resource utilization (minimum amount of time) in any scheduling interval.

Optimal solution methods for project scheduling under resource constraints may be obtained. Generally, the inclusion of resource constraints has the following effects :

 i. The total amount of scheduled slack is reduced.

 ii. The critical path may be altered. Furthermore, the zero slack activities may not necessarily lie along one or more continuous paths.

 iii. Earliest and latest-start schedules may not be unique. They depend on the particular rules that are used to resolve resource limitations.