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AIC Seminar Series

Direct Logic for Increased Safety in Reasoning about Large Software Systems

Carl HewittMIT EECS (emeritus)

Notice:  hosted by Richard Waldinger

Date:  Tuesday, July 18th 2006 at 2:30pm

Location:  EJ228  (Directions)


Large software systems are permeated with inconsistencies. Professional people deal with the pervasive inconsistency in large software systems on a daily basis. So how do they cope? They certainly don’t use classical logic because by the rules of classical logic, every proposition (including, for example, that “The moon is made of green cheese”!) follows from a contradiction. We need systems that don’t blow up in the face of inconsistencies and have developed Direct Logic with this in mind. Goals for Direct Logic include:

  • Formalize a notion of “direct” inference.
  • Support nontrivial inconsistent theories.
  • Formalize standard logical operators and connectives in terms of direct inference.
  • Support all “natural” deductive reasoning in theories that does not blow up in the face of an inconsistency.
  • Increased safety in reasoning about large software systems.
This talk explains how Direct Logic has been developed to be tolerant of contradictions by imposing a couple of intuitive restrictions on classical logic. In Direct Logic, there are theories which are inconsistent but nevertheless nontrivial because irrelevancies cannot be inferred from contradictions. Gödel's incompleteness theorem applies only to consistent theories. A contribution of this talk is to generalize the incompleteness theorem to nontrivial inconsistent theories. Since it includes the nondeterministic λ calculus, reflection, and mathematical induction in addition to its other inference capabilities, Direct Logic is a very powerful Logic Programming language. Nevertheless, there are concurrent programs that are not equivalent to any Direct Logic program. The Actor model of computation is used to characterize the incompleteness of Logic Programming.

   Bio for Carl Hewitt

Carl Hewitt is an emeritus professor from MIT. He is known for his design of Planner of which a subset Micro Planner implemented by Gerry Sussman, Eugene Charniak and Terry Winograd was used in Terry’s famous SHRDLU program. PROLOG subsequently reinvented some of the capabilities of Micro Planner. Carl and his students are also known for their work on Actors that are the universal primitives of concurrent computation. The Actor work built on Lisp, Simula-67, Smalltalk, and capability-based systems. History then repeated itself and versions of PROLOG based on message-passing reinvented some of the capabilities of Actors. Together with Bill Kornfeld, he developed the Scientific Community Metaphor. He has also made contributions in the areas of garbage collection, programming language design and implementation, open systems, negotiation forums and, multi-agency systems. Carl has worked to integrate sociology, anthropology, organization science, the philosophy of science, and services science into information science. He is also working on massive concurrency, the subject of a May 2005 seminar at Stanford and an October 2005 seminar at Berkeley.

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