Wegner's Lemma

"It is impossible to fully specify or test an interactive system designed to respond to external inputs."

-- Peter Wegner, Brown University ["Why Interaction is more powerful than algorithms," CACM 40(5):80-91, 1997]

Quick Summary

• A mathematical proof that any process that assumes known inputs, is doomed to failure when buildig interactive object-oriented systems.
• If silver bullets are interpreted as formal (or algorithmic) systems specifications, the nonexistence of silver bullets can actually be proved.
• Interaction is not expressible by algorithms.
• Complete specification must be replaced by partial specification of interfaces, views and modes of use.
• A system satisfies its requirements if it supports specified modes of use, even though correct behavior for a given mode of use is not guaranteed and complete system behavior for all possible modes of use is unspecifiable.
• From Rationalism to Empiricism: Social and scientific rationalism have common roots in the deep-seated human desire for certainty.
• Algorithms and Turing machines, like Cartesian thinkers, shut out the world during the process of problem solving.
• The sacrifice of completeness is frightening.
• The insight that the rationalism/empiricism dichotomy corresponds to algorithms and interactions... allow computing to be classified as empirical, along with physics and cognition.