Tractable Reasoning in Knowledge Representation Systems

This document addresses some problems raised by the well-known intractability of deductive reasoning in even moderately expressive knowledge representation systems. Starting from boolean constraint propagation (BCP), a previously known linear-time incomplete reasoner for clausal propositional theories, we develop fact propagation (FP) to deal with non-clausal theories, after motivating the need for such an extension. FP is specified using a confluent rewriting systems, for which we present an algorithm that has quadratic-time complexity in general, but is still linear-time for clausal theories. FP is the only known tractable extension of BCP to non-clausal theories; we prove that it performs strictly more inferences than CNF-BCP, a previously-proposed extension of BCP to non-clausal theories. We generalize a refutation reasoner based on FP to a family of sound and tractable reasoners that are "increasingly complete" for propositional theories. These can be used for anytime reasoning, i.e. they provide partial answers even if they are stopped prematurely, and the "completeness" of the answer improves with the time used in computing it. A fixpoint construction based on FP gives an alternate characterization of the reasoners in this family, and is used to define a transformation of arbitrary theories into logically-equivalent "vivid" theories -- ones for which our FP algorithm is complete. Our final contribution is to the description of tractable classes of reasoning problems. Based on FP, we develop a new property, called bounded intricacy, which is shared by a variety of tractable classes that were previously presented, for example, in the areas of propositional satisfiability, constraint satisfaction, and OR-databases. Although proving bounded intricacy for these classes requires domain-specific techniques (which are based on the original tractability proofs), bounded intricacy is one more tool available for showing that a family of problems arising in some application is tractable. As we demonstrate in the case of constraint satisfaction and disjunctive logic programs, bounded intricacy can also be used to uncover new tractable classes

Generating multimedia briefings: coordinating language and illustration

AbstractCommunication can be more effective when several media (such as text, speech, or graphics) are integrated and coordinated to present information. This changes the nature of media-specific generation (e.g., language or graphics generation), which must take into account the multimedia context in which it occurs. This paper presents work on coordinating and integrating speech, text, static and animated three-dimensional graphics, and stored images, as part of several systems we have developed at Columbia University. A particular focus of our work has been on the generation of presentations that brief a user on information of interes

Postinfectious cerebellar syndrome with paraneoplastic antibodies: An association or coincidence?

Cerebellar ataxia has a very broad differential diagnosis in adults, including paraneoplastic and postinfectious etiologies. We report a case of a 56-year-old male presented with right-sided cerebellar dysfunction preceded by fever and headache. He was diagnosed with subacute postinfectious cerebellar ataxia. Blood serology showed the presence of anti-amphiphysin and anti-Ri (ANNA-2, antineuronal nuclear autoantibody type 2) antibodies, which have a known association with cerebellar syndrome. The patient subsequently improved with the steroids. Although no evidence of an underlying tumor was found in the patient, the presence of the paraneoplastic antibodies remains a mystery. We suggest a probable association of these antibodies with the postinfectious cerebellar syndrome