Engineered Robustness by Controlled Hallucination

Jacob Beal, Gerald Jay Sussman

Most computer programs are brittle. They may have acceptable behavior for the range of applications that they are specified to work for, but they fail miserably for applications even slightly outside of that range. For example, a program may work well when its inputs are complete, but be unable to produce any sensible result if any of its inputs are missing or noisy. We propose a strategy for alleviating this kind of brittleness: because many programs are used repeatedly on a very sparse but highly structured subset of the possible inputs that might be provided, we can build wrappers that fill in missing or noisy data by inducing the missing information from the other inputs. We illustrate this strategy with a wrapper that acquires constraints on the graphical presentation of characters. When exposed to the first 317 words of "Pride and Prejudice," the constraints it acquires capture information that can be used to fill in missing or clarify noisy data in similarly presented text. This strategy of generalization wrappers can be applied recursively, to every subsystem of a large system, substantially improving the robustness of the system.

Submitted: Aug 25, 2008