Abstract: A programming environment can be modified to provide automatic support for reverting program memory states. Such memory reversions are used to provide automatic support for state-reversion, undo, redo, and abort operations for application programs written with the programming environment. Memory allocation code (e.g., functions, procedures, etc.) are modified to mark allocated memory as protected, and an exception handler is assigned to such memory. Attempts to access the memory cause an exception to be generated. This exception is caught, providing opportunity for the memory to be preserved before it is modified. Previous memory states can be retrieved by restoring such stored memory states. State-reversion can be effected by creating a new current memory state corresponding to a previous (e.g., retrieved) memory state.

Abstract: A programming environment can be modified to provide automatic support for reverting program memory states. Such memory reversions are used to provide automatic support for undo, redo, and abort operations for application programs written with the programming environment. Memory allocation code (e.g., functions, procedures, etc.) are modified to mark allocated memory as protected, and an exception handler is assigned to such memory. Attempts to access the memory cause an exception to be generated. This exception is caught, providing opportunity for the memory to be preserved before it is modified. Previous memory states can be retrieved by restoring such stored memory states.

Abstract: A reusable model of a three-dimensional object is created on a computer system. The reusable model includes model objects and internal constraints on the model objects. The internal constraints maintain the structure of the reusable model with respect to the three-dimensional object. The reusable model can have inputs that accept directed and non-directed external constraints with models using the reusable model. The inputs define the direct methods for modifying the structure of the reusable model. The reusable model can have outputs that have directed constraints with models using the reusable model. The outputs provide a direct method for using the structure of the reusable model to modify the structure of the model using the reusable model. Nondirected constraints may be associated between the model using the reusable model and the reusable model to position the reusable model in the model.