1. An article of manufacture comprising a computer readable storage medium including a program for manipulating instance data described by a base model, wherein the program is capable of causing operations to be performed, the operations comprising: receiving a ViewType, a root object representing an object of the base model, and an operation, wherein the ViewType references at least some classes, attributes, and associations of the base model as ViewType objects, an object in the ViewType corresponding to the object of the base model serves as a starting point for traversal of the ViewType, and wherein the operation is applied to one or more objects of the instance data; determining whether the ViewType and the root object are compatible based on an object type specified by a ViewList of a root of the ViewType, wherein the ViewList contains information about the classes in the base model; and in response to determining that the ViewType and the root object are compatible, applying the operation to the one or more objects of the instance data of the base model while by visiting each object of the instance data in a traversal path designated by a structure of the ViewType, wherein the structure of the ViewType is used as to identify which of the one or more objects of the instance data are to be processed.