1. A system for flexible workflow management, comprising: an apparatus including a storage medium having code segments stored thereon for execution of a workflow; a process modeling tool operable to create a workflow process model, the process model including a configurable task set that includes a plurality of tasks and a plurality of constraints that define relationships between the plurality of tasks, each constraint of the plurality of constraints corresponding to a constraint type of a plurality of constraint types, wherein the plurality of constraint types includes at least one structural constraint type and at least one containment constraint type; a constraints validation engine operable to: simplify a specification of the plurality of constraints for each said constraint by resolving intra-constraint conflicts for each said constraint type to provide a minimal specification for each said constraint of the constraint type, wherein for each said constraint type, said constraints validation engine is operable to resolve said intra-constraint conflicts by (1) examining the plurality of constraints for transitivities and redundancies, (2) where possible, capturing any transitivities and removing any redundancies detected, and (3) employing a minimum cover algorithm when the constraint type is structural and a truth table algorithm when the constraint type is containment; resolve inter-constraint conflicts between each of the plurality of constraint types, taking into account any redundancies and/or transitivities detected between the plurality of constraint types; and validate the plurality of tasks and the plurality of constraints such that each of the plurality of tasks are includable in at least one task subset without violating any of the plurality of constraints in each of the minimal specifications of the plurality of constraints; and a workflow engine operable to create an open instance by copying the process model, and further operable to activate the configurable task set during execution of the open instance, and to thereby compile and execute an instance template including a selected task subset of the plurality of tasks.