1. A method of scheduling submission of work units for execution on a data processing system, the method including the steps of: estimating a plurality of attributes for each work unit, each attribute being indicative of the usage of a corresponding resource of the system by the work unit, combining the attributes of each work unit into a single cumulative index, the index being indicative of a total usage of the resources of the system by the work unit, defining a plan of execution of the work units for optimizing the total usage of the resources of the system according to the corresponding cumulative indexes, and submitting the work units of the plan.