1. A computer-implemented method of computer-aided design (CAD) comprising: creating a computer-generated three-dimensional (3D) model in a broken view state, by: removing an area of the computer-generated 3D model in an unbroken view state to create the computer-generated 3D model in the broken view state; implementing a mapping between the computer-generated 3D model in the unbroken view state and the computer-generated 3D model in the broken view state to enable operations performed on the computer-generated 3D model in the broken view state to utilize data defining the computer-generated 3D model in the unbroken view state, wherein the mapping maintains a relationship between data defining the computer-generated 3D model in the unbroken view state and data defining the computer-generated 3D model in the broken view state; identifying entities in the computer-generated 3D model in the unbroken view state using identifying data, wherein each identified entity is one of a topological entity and a geometric entity; constructing one or more data structures to hold the data defining the computer-generated 3D model in the unbroken view state and to hold the data defining the computer-generated 3D model in the broken view state; and utilizing the identifying data and the mapping to determine from which identified entity in the computer-generated 3D model in the unbroken view state an entity in the computer-generated 3D model in the broken view state is derived, results of the determination enabling an operation performed on the computer-generated 3D model in the broken view state to access from the data structures and use data defining the computer-generated 3D model in the unbroken view state.