1. A method of modeling a real-world modeled system with a system model in a data processing system, the method comprising: the data processing system constructing in the system model a multi-level hierarchy of Capabilities in the real-world system, each Capability including a Verb specifying an action and an Object acted on by the Verb; the data processing system constructing in the system model one or more multi-level Performer hierarchies, each Performer hierarchy including a plurality of Performers each having a specified association with an associated lifecycle defined in the system model and a specified association with at least one associated Capability defined in the multi-level hierarchy of Capabilities, wherein each of the at least one associated Capability is one of a set including a provided Capability provided by the Performer and a required Capability required by the Performer, and wherein at least one Performer in the one or more multi-level Performer hierarchies has an associated provided Capability and at least one Performer in the one or more multi-level Performer hierarchies has an associated required Capability; the data processing system constructing in the system model a multi-level Location hierarchy associating one of a plurality of Locations with each Performer in the one or more multi-level Performer hierarchies; the data processing system constructing in the system model a plurality of Capability Instances defining requirement and provision of Capabilities by Performers in the one or more multi-level Performer hierarchies, wherein each of the plurality of Capability Instances specifies a particular Capability defined in the multi-level hierarchy of Capabilities, a subject Performer that requires the particular Capability, and a delivering Performer that delivers the particular Capability to the subject Performer; in response to a user input identifying, for a proposed Capability Instance, a selected subject Performer, a selected delivering Performer and a selected Capability, the data processing system validating, by reference to the one or more multi-level Performer hierarchies, that the selected delivering Performer can provide the selected Capability to the selected subject Performer; in response to validating that the selected delivering Performer can provide the selected Capability to the selected subject Performer, the data processing system constructing the proposed Capability Instance as one of the plurality of Capability Instances in the system model; in response to failure of the validating, the data processing system rejecting the proposed Capability Instance from inclusion in the system model; and in response to a query specifying a Location and a simulated time, the data processing system outputting a view of the system model for the specified Location and simulated time.