15. The system according to claim 13 , further comprising instructions which are executable, using the processor of the computer, for: creating an identity for a particular one of the resources, using the naming rule for the class that corresponds to the resource type of the particular resource; and storing the created identity as the value of the instance identity property for an instance which represents the particular resource.
13. A system for uniquely identifying resources, comprising: a hierarchical schema that models the resources, wherein classes in the hierarchical schema correspond to resource types and wherein instances in the hierarchical schema represent individual resources, each instance being defined according to a class definition of a selected one of the classes that corresponds to the resource type of the individual resource represented by the instance; and instructions which are executable, using a processor of a computer, for defining, in the class definition of a topmost class of the hierarchical schema, a naming rule property and an instance identity property, the naming rule property for storing a naming rule for each of the classes in an associated naming rule property value, and the instance identity property for storing an identity of each of the instances in an associated instance identity property value, wherein: each class at levels of the hierarchical schema beneath the topmost class inherits the naming rule property and the instance identity property, thereby requiring each class in the hierarchical schema to store a class-specific naming rule as the value of the naming rule property and each instance of each of the classes to store an instance-specific identity as the value of the instance identity property; the naming rule for each class specifies at least one property defined in the class definition of that class, and is used for creating the identity for each instance of that class; and the naming rule for each of the classes is selected to ensure that the identity created for each of the instances of each of the classes is unique within the hierarchical schema.