1. A computer-implemented method of uniquely identifying resources, comprising: modeling the resources using a hierarchical schema, 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 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.
3. The method according to claim 1 , wherein: the naming rule a selected one of the classes further specifies a scoping context selected to ensure that each of the identities created using that naming rule are unique within the scoping context; and the value of the instance identity property for each of the instances created using that naming rule further specifies the scoping context.