1. An interactive workflow scheduling system comprising at least one programmed computer configured to provide: a front-end platform supporting a web-portal to an interactive workflow scheduler; a back-end hardware platform supporting a real-time scheduling application; an interface arranged to support data communication between the web-portal provided by the front-end platform and the real-time scheduling application provided by said back-end platform over a communications network; an interface arranged to enable user input of one or more user-specified constraint conditions when a user-requested workflow request is generated during an on-line communications session between the user and the front-end platform; wherein the interactive workflow scheduler generates an abstract instantiation of a workflow responsive to said workflow request, the abstract instantiation of the workflow comprising a plurality of actions having a predetermined dependency relationship, wherein the interactive workflow scheduling system is arranged to enable user-specified constraint conditions to be received via said web-portal provided on the front-end platform to control in real-time the configuration by said real-time scheduling application of said abstract instantiation of said workflow when generating a scheduled workflow, wherein said real-time scheduling application includes: a workflow generator arranged to generate a scheduled workflow in real-time dependent on said user-specified constraint conditions for the abstract instantiation of the workflow generated by said interactive workflow scheduler during the on-line communications session between the front-end platform and back-end platform, the scheduled workflow which is generated satisfying said one or more user-specified constraint conditions, and wherein the real-time scheduler application optimizes the global utilization of the resources required to fulfill said user-requested constraints for said abstract instantiation of said workflow by processing in parallel the resource requirements of each of said plurality of actions required by the scheduled workflow during said on-line communications session, wherein a scheduled workflow for said abstract instantiation of said workflow is regenerated responsive to reiterated user constraint conditions being inputted during said communications session.