Provided is a computer-implemented method for updating a 3D model. The method comprises providing an operation undergone by the 3D model, an old input graph of the 3D model before undergoing the operation, an old output graph of the 3D model corresponding to an application of the operation to the old input graph, and a new input graph of the operation. The new input graph is generated as a result of a modification of the 3D model. The method also comprises computing a double push-out rewriting rule that specifies a part of the old input graph to be replaced, a part of the new input graph to replace the part of the old input graph. The rewriting rule also specifies an interface which is a part common to the part of the old input graph, the part of the new input graph, and the old output graph. The method further comprises applying the rewriting rule directly on the old output graph. This transforms the old output graph to a new output graph representing an updated 3D model of the real world object. The method is an improvement to updating a 3D model in a CAD system.